0021-972X/90/7004-0859$02.00/0 Journal of Clinical Endocrinology and Metabolism Copyright © 1990 by The Endocrine Society
Vol. 70, No. 4 Printed in U.S.A.
Prevalence of a-Subunit Hyper secretion in Patients with Pituitary Tumors: Clinically Nonfunctioning and Somatotroph Adenomas* DANIEL S. OPPENHEIM, ARNOLD R. KANA, JANGBIR S. SANGHA, AND ANNE KLIBANSKI Neuroendocrine Unit and the General Clinical Research Center, Massachusetts General Hospital, Boston, Massachusetts 02114
ABSTRACT. Hypersecretion of the pituitary glycoprotein hormone a-subunit has been reported in pituitary adenomas, particularly in clinically nonfunctioning tumors and somatotroph adenomas. However, the prevalence of such hypersecretion has not been precisely defined. Using both a new highly sensitive and specific monoclonal antibody assay and a polyclonal antibody assay, serum levels of free a-subunit were compared in 63 unselected patients with these tumors, 19 patients with acromegaly, and 95 normal controls. In all patients the monoclonal assay detected a significantly greater number of subjects with elevated a-subunit levels than did the polyclonal assay (21 us. 14; P < 0.01). Fourteen of the 63 patients with clinically nonfunctioning tumors (22%) had elevated serum a-subunit levels in the monoclonal assay vs. 11
(17%) in the polyclonal assay. Among the 19 patients with acromegaly, the prevalence was 7 (37%) and 3 (16%) using the monoclonal and polyclonal assays, respectively.Twenty-eight (44%) of the patients with clinically nonfunctioning pituitary adenomas were female. Eleven (39%) of the women were under 45 yr old, as were 10 (29%) of the men. We conclude that the prevalence of free a-subunit hypersecretion in patients with clinically nonfunctioning and somatotroph adenomas may be higher than previously recognized, and that a sensitive and specific monoclonal antibody free a-subunit assay may provide a useful tumor marker in these patients. The prevalence of clinically nonfunctioning pituitary tumors among younger men and women may also have been previously underestimated. (J Clin Endocrinol Metab 70: 859-864, 1990)
T
HE MAJORITY of pituitary adenomas produce clinical syndromes resulting from the direct effects of hormone hypersecretion by the tumor. However, 2530% of pituitary tumors produce no such syndrome and have been termed clinically nonfunctioning. Recently, it has been reported that a substantial number of clinically nonfunctioning pituitary tumors may synthesize and secrete intact glycoprotein hormones or their free subunits (1-3). This has been shown by a number of in vitro techniques, including cell culture (4-7), analysis of specific RNA species (8-10), and immunocytochemistry (11-13) of surgically excised tumor tissue. Elevated levels of glycoprotein hormones or subunits in the serum of patients with clinically nonfunctioning pituitary tumors has been described (3), but the prevalence of such elevation has not been precisely determined. The presence of such tumor markers is extremely useful for both diagnosis and follow-up. Despite such secretion by these tumors, they are justifiably referred to as clinically non-
functioning because a characteristic clinical syndrome resulting from tumoral hypersecretion has not been identified. Many such patients are found to have mild hyperprolactinemia, which results from pituitary stalk compression and presumed decreased hypothalamic dopaminergic inhibition of PRL secretion. This is confirmed by disproportionately mild hyperprolactinemia relative to tumor size and the absence of immunocytochemically detectible PRL in excised tumor tissue. The pituitary glycoprotein hormones LH, FSH, and TSH are dimeric proteins composed of a common asubunit and a specific /?-subunit. Free a-subunit is detectable in the serum of normal individuals (14, 15) and is secreted by both pituitary thyrotrophs and gonadotrophs (16). a-Subunit levels are elevated in states of increased TSH or gonadotropin secretion, such as in primary hypothyroidism (17) or the menopause (18), and may increase with the administration of GnRH and TRH (19). In addition, ectopic production of free a-subunit by nonpituitary neoplasms has been demonstrated (20, 21). An important advance in the understanding of glycoprotein hormone production in neoplastic tissue has been the finding of elevated serum levels of free a-subunit in patients with pituitary tumors secreting gonadotropins,
Received June 13,1989. Address requests for reprints to: Anne Klibanski, M.D., Massachusetts General Hospital, Boston, Massachusetts 02114. * This work was supported in part by NIH Grants DK-40947, RR01066, and DK-07028.
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OPPENHEIM ET AL.
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TSH, and, rarely, ACTH or PRL (4, 9, 22-30). A subset of patients with acromegaly have been found to cosecrete free a-subunit and GH (28, 30), but the frequency of this cosecretion and its clinical significance have not been determined. In addition, in a subset of pituitary tumors, elevation of serum free a-subunit levels occurs without hypersecretion of other pituitary hormones (24, 31, 32). Free a-subunit has proved useful as a tumor marker in patients with clinically nonfunctioning pituitary tumors. Surgical resection (22, 31) and external radiation (28) of a-subunit-secreting pituitary adenomas have been shown to decrease serum a-subunit levels, and subsequent increases in these levels may indicate tumor growth or recurrence. The measurement of serum asubunit levels may also have importance as an indication of tumor response to medical therapy (33), such as with analogs of dopamine (29) or somatostatin (34). Previous studies of a-subunit secretion have used polyclonal antibodies raised against purified a-subunit. Such antibodies show variable levels of cross-reactivity with intact LH, FSH, and TSH (15, 17, 35, 36). Thus, in states of elevated glycoprotein hormone secretion, it may be difficult to distinguish a-subunit immunoreactivity due to cross-reactivity from that due to abnormal asubunit hypersecretion. Thotakura and Bahl (37) have described a monoclonal antibody that is highly sensitive and specific for uncombined a-subunit. The application of an assay using such an antibody could eliminate many of the problems of intact glycoprotein hormone cross-reactivity and allow several questions to be addressed. 1) What is the prevalence of free asubunit secretion by clinically nonfunctioning pituitary adenomas? 2) Does monoclonal a-subunit immunoreactivity represent a more sensitive tumor marker? 3) Can this assay more readily differentiate abnormal from normal states of a-subunit hypersecretion? 4) What is the prevelence of a-subunit cosecretion in acromegaly? 5) Does such cosecretion affect the natural history of the disease or the response to therapy? We studied two groups of patients with pituitary tumors: a group with clinically nonfunctioning adenomas and a group with somatotroph adenomas. Using the newly developed monoclonal anti-a-subunit antibody assay, we compared these two groups of pituitary tumor patients to normal men, premenopausal women, and postmenopausal women. Materials and Methods Hormone assays Polyclonal a-subunit RIAs were performed as previously described (14). The detection limit for a-subunit is 0.2 ng/tube, with cross-reactivities of 2.5-3.0% with purified intact LH and FSH. Monoclonal a-subunit RIAs were performed using a kit
JCE & M • 1990 Vol70«No4
(Biomerica, Inc., Newport Beach, CA), using a purified monoclonal anti-a-subunit antibody (37). The detection limit for asubunit is 0.05 ng/tube. The cross-reactivities with intact glycoprotein hormones are all less than 0.2%, and those with purified subunits of human LH, FSH, and TSH are less than 0.1%. LH, FSH, and TSH immunoradiometric assays were perfomed using kits from Celltech Diagnostics Ltd. (Slough, Berkshire, United Kingdom). The cross-reactivities of free asubunit in the LH and FSH assays are 0.13% and 0.03%, respectively. Statistical methods Analysis of variance was used to compare the mean a-subunit levels among various groups. Dunnett's test was used to compare the mean a-subunit level of the patients to that of the controls. Macnamar's test was used to compare the number of patients with elevated a-subunit levels detected with the monoclonal and polyclonal a-subunit assays. Study subjects We studied 63 patients with clinically nonfunctioning pituitary adenomas and 19 patients with acromegaly, and compared these patients with 95 normal controls. The patients with clinically nonfunctioning pituitary adenomas represented sequential patients undergoing transsphenoidal pituitary surgery at the Massachusetts General Hospital. Immunocytochemical staining for PRL and GH was negative in all cases. There were 35 male and 28 female patients. None had clinical evidence of acromegaly or Cushing's syndrome, and all had a pathologically confirmed diagnosis of pituitary adenoma at surgery. The age range of the male patients was 24-74 yr (mean ± SD, 52.0 ± 13.1 yr), and that of the female patients was 16-81 yr (mean, 52.2 ± 17.1 yr). Ten of the 35 male patients (29%) were less than 45 yr old. The female patients were divided into 3 groups for analysis: less than 45 yr old (premenopausal age range), greater than 50 yr old with serum FSH and/or LH levels in the normal postmenopausal range (>30 IU/L), and greater than 50 yr old with serum gonadotropin levels below the postmenopausal range. (There were no female patients 45-50 yr old.) This was done to allow comparison of a-subunit levels with those of the appropriate control group; because free a-subunit is cosecreted with gonadotropins and, therefore, may be elevated in postmenopausal women, we compared the a-subunit levels of the older pituitary tumor patients who had elevated gonadotropin levels with those of the postmenopausal control women, and we compared the a-subunit levels of the older pituitary tumor patients who had inappropriately low gonadotropin levels (30 IU/L), 47-73 yr old (mean, 55.2 ± 6.3 yr). The premenopausal women were studied during 3 phases of the menstrual cycle: 8 in the early follicular phase, 10 in the preovulatory phase, and 10 in the luteal phase. All women had a history of normal menstual cycles, and ovulation was confirmed by basal body temperature recording and luteal phase serum progesterone concentrations above 16 nmol/L (>5 ng/mL). None of the controls had any medical illness, and none was taking medication. The mean LH and FSH levels in the control men were 5.0 ± 2.4 and 4.0 ± 3.8 IU/L, respectively.
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TABLE 2. Clinical features of 28 women with clinically nonfunctioning pituitary adenomas No. (%) Age: Gonadotropins:0
50yr
' High gonadotropins = serum LH and/or FSH levels above 30 IU/ L. 6
On formal neuroophthalmological examination. Greater than 10 mm on computed tomographic or magnetic resonance imaging scanning. c
Results Clinical presentation Table 1 summarizes the clinical features of the male study patients. Serum PRL was mildly elevated in 26 of the 35 male nonfunctioning tumor patients (74%) and was greater than 20 ng/L in only 6 (17%). One male patient had evidence of cryptic hypercortisolism (positive ACTH immunocytochemistry and elevated serum cortisol levels without clinical evidence of Cushing's syndrome). None of the men with clinically nonfunctioning pituitary tumors had elevated serum LH levels, and 5 had elevation of serum FSH concentrations. Eleven of the 28 female patients (39%) with clinically nonfunctioning tumors (Table 2) were under 45 yr old. Two had regular menstrual periods, 6 had oligmenorrhea, and 3 were amenorrheic. All 11 of the younger female TABLE 1. Clinical features of 35 men with clinically nonfunctioning pituitary adenomas No. (%) Headache Hypogonadism0 Visual field defect6 Hyperprolactinemia Central hypothyroidism at presentation Central hypoadrenalism at presentation Pituitary apoplexy at presentation Incidental finding Macroadenomac 0
16 (46) 27 (77) 29 (83) 26 (74) 9(26) 10 (29) 3(9) 2(6) 35 (100)
Decreased sexual function and serum testosterone below 10.4 nmol/ L (300 ng/dL). 6 On formal neuroophthalmological examination. e Greater than 10 mm on computed tomographic or magnetic resonance imaging scanning.
patients had mild hyperprolactinemia (>20 /ng/L), and 6 had galactorrhea. Of the 17 women over 50 yr old with clinically nonfunctioning pituitary tumors (Table 2), 7 were found to have the expected elevation of serum LH and FSH (>30 IU/L), but the other 10 had gonadotropin levels below the normal postmenopausal range. Sixteen patients were amenorrheic, and 1 had oligomenorrhea and intermittently elevated gonadotropin levels suggestive of the perimenopause. There were 11 patients with mild hyperprolactinemia, but none had galactorrhea. One woman and three men had tumoral hypersecretion of TSH (with serum TSH levels of 5.3, 5.9, 6.9, and 9.6 mU/L) and positive TSH/5 immunocytochemistry, but were clinically and biochemically euthyroid. a-Subunit levels Table 3 shows the a-subunit levels measured with both the monoclonal antibody and the polyclonal antibody in patients and controls. There was no statistically significant difference between the mean a-subunit concentrations, measured with either the monoclonal or the polyclonal antibody, of any patient group and those of the relevant control group. When the 28 premenopausal control women were subdivided on the basis of the phase of the menstrual cycle, there was no difference in the mean a-subunit levels, measured with either antibody, among these 3 groups (data not shown). Among the normal controls, the postmenopausal women had significantly higher a-subunit levels in both assays than the men and the premenopausal women.
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OPPENHEIM ET AL.
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TABLE 3. Serum a-subunit levels in 82 patients with pituitary adenomas and 95 controls using monoclonal and polyclonal antibodies Monoclonal (ng/L)
Polyclonal (ng/L)
n
Range
Mean
SD
35 11
60-20,000 90-3,700
1,010
3,360 1,050
Range
Mean
SD
300-52,700 590-14,200
3,110 2,170
9,010 4,010
400-1,700 1,400-17,700
1,010 4,200
5,980
700-26,700 540-2,300
4,040 1,130
8,510 2,220 2,830
Nonfunctioning tumors (n = 63) Men
Women 50 yr Low gonadotropins High gonadotropins" Acromegaly (n = 19) Men Women 50 yr Low gonadotropins High gonadotropins Control
10 7
100-3,700 270-8,500
9 6
120-10,000 70-630
2 2
120-1,100 610-2,700
Men
35
Premenopausal women Postmenopausal women
28
70-450 50-460 290-1,500
1
32
580 300
150
1,680
3,010
1,360
3,240
290
210
610
690 1,480
560-3,700 3,300-7,300
2,130 5,300
300-1,700 420-1,600 1,200-7,100
790
300
870
350
3,380
1,640
1,660 190
90
220
110
820
380
440
700
High gonadotropins = serum LH and/or FSH levels above 30 IU/L.
TABLE 4. Number of patients with pituitary tumors and elevated serum a-subunit concentration No. (%) Nonfunctioning tumors Men Women 50 yr Low gonadotropins High gonadotropins0 Total Acromegalics Men
Women 50 yr Low gonadotropins High gonadotropins Total All patients
Monoclonal
Polyclonal
11
9(26) 2(18)
6(17) 2(18)
10 7 63
2 (20) 1(14) 14 (22)
2(20) 1(14) 11(17)
9 6
4(44) 1(17)
2(22) 0(0)
2 2 19
1(50) 1(50) 7(37)
0(0) 1(50) 3(16)
82
21 (26)
14 (17)
35
Elevated serum a-subunit concentration = greater than 2 SD above the mean control concentration. 0 High gonadotropins = serum LH and/or FSH greater than 30 IU/ L.
Table 4 shows the number of pituitary tumor patients in each clinical group who had serum a-subunit levels greater than 2 SD above the mean of the appropriate control group. In the pituitary tumor patients, the monoclonal antibody assay detected a significantly greater number of patients with serum a-subunit elevation than did the polyclonal antibody assay (P < 0.01). Fourteen of the 63 patients with clinically nonfunctioning adenomas (22%) had elevated serum levels of free a-subunit using the monoclonal antibody assay, 3 more than were found using the polyclonal assay (17%). All 3 of these
patients were male. Among the 19 acromegalic patients, 7 (37%) had elevated serum a-subunit levels using the monoclonal assay, whereas 4 had such elevations using the polyclonal assay (21%). All 3 of the acromegalic patients with TSH cosecretion had serum a-subunit elevations in the monoclonal antibody assay. In all, the monoclonal a-subunit assay detected 7 more patients with elevated serum a-subunit levels than did the polyclonal assay.
Discussion We have studied the prevalence of a-subunit hypersecretion in 63 unselected patients with clinically nonfunctioning pituitary adenomas and 19 patients with acromegaly. We have show that, using a highly specific monoclonal anti-a-subunit antibody assay, a significantly greater number of pituitary tumor patients had asubunit hypersecretion (P < 0.01). Twenty-two percent of patients with clinically nonfunctioning pituitary adenomas have elevated serum levels of free a-subunit in the monoclonal a-subunit assay. The monoclonal assay was more sensitive than the polyclonal assay, detecting an additional 3 patients (9%) with a-subunit hypersecretion. a-Subunit hypersecretion was even more prevalent in acromegalic patients (37%), with 4 more patients (21%) being detected in the monoclonal assay than in the polyclonal assay. The prevalence of a-subunit hypersecretion in patients with clinically nonfunctioning pituitary adenomas is not well established. Most other reports have suggested a low frequency of such hypersecretion (11, 22, 24, 28, 30). However, Snyder (3) found that of 139 consecutive male patients with pituitary adenomas, 53 were nonsecreting,
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a-SUBUNIT SECRETION IN PITUITARY TUMORS 8 secreted a-subunit only, and 11 of the 23 FSH-secreting tumors cosecreted free a-subunit. This yields a prevalence of a-subunit hypersecretion in patients with clinically nonfunctioning pituitary tumors of 23%, a result similar to ours. Fourteen percent of our male patients with clinically nonfunctioning pituitary tumors had FSH hypersecretion compared with 17% in Snyder's series (3). a-Subunit cosecretion by somatotroph adenomas has been described (28, 30, 38), but its prevalence is not known. MacFarlane et al. (28) found serum a-subunit elevation in 13 of 46 acromegalic patients (28%), BeckPeccoz et al. (38) found such elevation in 4 of 22 acromegalic patients (18%), and Ishibashi et al. (30) in 5 of 58 (9%). Other reports are primarily case reports (29, 34) rather than large series. These frequencies are lower than our result of 37% using a monoclonal antibody assay and suggest that a monoclonal assay is a more sensitive method of detecting a-subunit hypersecretion in patients with acromegaly as well as in clinically nonfunctioning tumors. There is evidence that GH and a-subunit may coexist within the same tumor cells and, in some cases, within the same secretory granules in patients with acromegaly and a-subunit hypersecretion (39). Two additional findings in our series were the number of patients in the younger age group and the number of female patients. Nearly half (44%) of our unselected patients were women, 39% of whom were under 45 yr old, the youngest being 16 yr old. Furthermore, 40% of the men with clinically nonfunctioning pituitary tumors were under the age of 50 yr, the youngest of whom was 24 yr old. These results differ from most previously reported series, in which the majority of such tumors have been found in men over 40 yr old (2, 3, 24, 40, 41). The diagnosis of these tumors may be more difficult in the older female population because of the absence of an early clinical marker such as oligoamenorrhea and because of the normal elevation of serum gonadotropin levels found after menopause. We conclude that a-subunit hypersecretion may be more common than previously recognized among patients with clinically nonfunctioning pituitary tumors or acromegaly. The sensitive and specific monoclonal asubunit assay may prove to be a useful tool in providing a tumor marker in a significant number of patients with these tumors and may allow for more precise diagnosis, characterization, and follow-up. The biological and clinical significance of a-subunit cosecretion in patients with pituitary tumors is not known at this time. Whether such cosecretion is of importance in the pathogenesis of these tumors or whether it alters the clinical course or response to therapy deserves further study.
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References 1. Klibanski A. Nonsecreting pituitary tumors. Endocrinol Metab Clin North Am. 1987;16(Suppl 3):793-804. 2. Snyder PJ. Gonadotroph cell pituitary adenomas. Endocrinol Metab Clin North Am. 1987;16(Suppl 3):755-64. 3. Snyder PJ. Gonadotroph adenomas of the pituitary. Endocr Rev. 1985;6:552-63. 4. Mashiter K, Adams E, Van Noorden S. Secretion of LH, FSH and prolactin shown by cell culture and immunocytochemistry of human functionless pituitary adenomas. Clin Endocrinol (Oxf). 1981;15:103-12. 5. Asa SL, Gerrie BM, Singer W, et al. Gonadotropin secretion in vitro by human pituitary null cell adenomas and oncocytomas. J Clin Endocrinol Metab. l986;62:1011-9. 6. Beitins IZ, Lipson LG, McArthur JW. Immunoreactive LH, FSH and their subunits in tissue culture media from normal and adenomatous, human pituitary fragments. J Clin Endocrinol Metab. 1977;45:1271-80. 7. Snyder PJ, Hildegarde MB, Phillips JL, et al. Comparison of the hormonal secretory behavior of gonadotroph cell adenomas in vivo and in culture. Clin Endocrinol Metab. 1985;61:1061-5. 8. Jameson JL, Klibanski A, Black PM, et al. Glycoprotein hormone genes are expressed in clinically non-functioning pituitary adenomas. J Clin Invest. 1987;80:1472-8. 9. Klibanski A, Deutsch PJ, Jameson JL, et al. Luteinizing hormonesecreting pituitary tumor: biosynthetic characterization and clinical studies. J Clin Endocrinol Metab. 1987;64:536-42. 10. Klibanski A, Shupnik MA, Bikkal HA, et al. Dopaminergic regulation of a-subunit secretion and mRNA levels in a-secreting pituitary tumors. J Clin Endocrinol Metab. 1988;66:96-102. 11. Black PM, Hsu DW, Klibanski A, et al. Hormone production in clinically nonfunctioning pituitary adenomas. J Neurosurg. 1987;66:244-50. 12. Kovacs K, Horvath E, Ryan N, et al. Null cell adenoma of the pituitary. Virchows Arch Pathol Histol. 1980;387:165-74. 13. Landolt AM, Heitz PU. Alpha-subunit-producing pituitary adenomas: immunocytochemical and ultrastructural studies. Virchows Arch Pathol Anat. 1986;409:417-31. 14. Kourides IA, Weintraub BD, Levko MA, Maloof F. Alpha and beta subunits of human thyrotropin: purification and development of specific radioimmunoassay. Endocrinology. 1974;94:1411-21. 15. Papapetrou PD. Circulating a-subunit of glycoprotein hormones in normal subjects and its relationship to the LH and FSH serum levels. Acta Endocrinol (Copenh). 1982;(Suppl) 248:1-2. 16. Kourides IA, Weintraub BD, Re RN, Ridgway EC, Maloof F. Thyroid hormone, oestrogen, and glucocorticoid effects on two different pituitary glycoprotein hormone alpha subunit pools. Clin Endocrinol (Oxf). 1978;9:535-42. 17. Kourides IA, Weintraub BD, Ridgway EC, Maloof F. Pituitary secretion of free alpha and beta subunit of human thyrotropin in patients with thyroid disorders. J Clin Endocrinol Metab. 1975;40:872-85. 18. Laburthe MC, Dolais JR, Rosselin GE. Evidence for circulating a subunits of pituitary gonadotropins in plasma. J Clin Endocrinol Metab. 1973;37:156-9. 19. Hagen C, McNeilly AS. Changes in circulating levels of LH, FSH, LH/3- and a-subunit after gonadotropin-releasing hormone, and of TSH, LH/3- and a-subunit after thyrotropin-releasing hormone. J Clin Endocrinol Metab. 1975;41:466-70. 20. Blackman MR, Weintraub BD, Rosen SW, Kourides IA, Steinwascher K, Gail MH. Human placental and pituitary glycoprotein hormones and their subunits as tumor markers: a quantitative assessment. J Natl Cancer Inst. 1980;65:81-92. 21. Papappetrou PD, Anagnostopoulos NI. A gonadotropin and asubunit suppression test for the assessment of the ectopic production of human chorionic gonadotropin and its subunits after the menopause. J Clin Endocrinol Metab. 1985;60:1187-95. 22. Kourides IA, Weintraub BD, Rosen SW, et al. Secretion of alpha subunit of glycoprotein hormones by pituitary adenomas. J Clin Endocrinol Metab. 1976;43:97-106. 23. Demura R, Jibiki K, Kubo O, et al. The significance of a-subunit
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OPPENHEIM ET AL. as a tumor marker for gonadotropin-producing adenomas. J Clin Endocrinol Metab. 1986;63:564-9. Ridgway EC. Glycoprotein hormone production by pituitary tumors. Prog Endocr Res Ther. 1984;l:343-63. Borges JLC, Ridgway EC, Kovacs K, et al. FSH-secreting pituitary tumor with concomitant elevations of serum alpha-subunit levels. J Clin Endocrinol Metab. 1984;58:937-41. Chapman AJ, MacFarlane IA, Shalet SM, et al. Discordant serum a-subunit and FSH concentrations in a woman with a pituitary tumour. Clin Endocrinol (Oxf). 1984;21:123-9. Snyder PJ, Bashey JM, Kim SU, et al. Secretion of uncombined subunits of LH by gonadotroph cell adenomas. J Clin Endocrinol Metab. 1984;59:1169-75. MacFarlane IA, Beardwell CG, Shalet SM, et al. Glycoprotein hormone alpha-subunit secretion in patients with pituitary adenomas: influence of external irradiation. Clin Endocrinol (Oxf). 1980;13:215-22. MacFarlane IA, Beardwell CG, Shalet SM, et al. Glycoprotein hormone alpha-subunit secretion in patients with pituitary adenomas: influence of TRH, LRH, and bromocriptine. Acta Endocrinol (Copenh). 1982;99:487-92.
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hormone-secreting pituitary tumors. Endocrinol Metab Clin North Am. 1989;18(Suppl 2):339-58. Sassolas G, Serusclat P, Claustrat B, et al. Plasma alpha-subunit levels during the treatment of pituitary adenomas with the somatostatin analogue (SMS 201-995). Horm Res. 1988,29:124-8. Snyder PJ, Johnson J, Muzyka R. Abnormal secretion of glycoprotein alpha-subunit and FSH/3-subunit in men with pituitary adenomas and FSH hypersecretion. J Clin Endocrinol Metab. 1980;51:579-84. Hagen C, McNeilly AS. The specificity and application of radioimmunoassay for the a-subunit of luteinizing hormone in man. Acta Endocrinol (Copenh). 1975;41:466-70. Thotakura NR, Bahl OP. Highly specific and sensitive hybridoma antibodies against the a-subunit of human glycoprotein hormones. Endocrinology. 1985;117:1300-8. Beck-Peccoz P, Bassetti M, Spada A, et al. Glycoprotein hormone a-subunit response to growth hormone (GH)-releasing hormone in patients with active acromegaly. Evidence for a-subunit and GH coexistence in the same tumor cell. J Clin Endocrinol Metab. 1985;61:541-6. Osamura RY, Watanabe K. Immunohistochemical colocalization
30. Ishibashi M, Yamaji T, Takaku F, Teramoto A, Fukushima T.
of growth hormone (GH) and a subunit in human GH secreting
Secretion of glycoprotein hormone a-subunit by pituitary tumors. J Clin Endocrinol Metab. 1987;64:1187-93. 31. Ridgway EC, Klibanski A, Ladenson PW, et al. Pure alpha-secreting pituitary adenomas. N Engl J Med. 1981;304:1254-9. 32. Klibanski A, Ridgway EC, Zervas NT. Pure alpha subunit-secreting pituitary tumors. J Neurosurg. 1983;59:585-9. 33. Oppenheim DS, Klibanski A. Medical therapy of glycoprotein
pituitary adenomas. Vichows Arch Pathol Anat. 1987;411:323-30. 40. Snyder PJ, Bigdeli J, Gardner DF, et al. Gonadal function in fifty men with untreated pituitary adenomas. J Clin Endocrinol Metab. 1979;48:309-14. 41. Ebersold MJ, Quast LM, Laws ER, et al. Long-term results in transsphenodial removal of nonfunctioning pituitary adenomas. J Neurosurg. 1986;64:713-9.
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Vol. 70, No. 4 Printed in U.S.A.
Prevalence of a-Subunit Hyper secretion in Patients with Pituitary Tumors: Clinically Nonfunctioning and Somatotroph Adenomas* DANIEL S. OPPENHEIM, ARNOLD R. KANA, JANGBIR S. SANGHA, AND ANNE KLIBANSKI Neuroendocrine Unit and the General Clinical Research Center, Massachusetts General Hospital, Boston, Massachusetts 02114
ABSTRACT. Hypersecretion of the pituitary glycoprotein hormone a-subunit has been reported in pituitary adenomas, particularly in clinically nonfunctioning tumors and somatotroph adenomas. However, the prevalence of such hypersecretion has not been precisely defined. Using both a new highly sensitive and specific monoclonal antibody assay and a polyclonal antibody assay, serum levels of free a-subunit were compared in 63 unselected patients with these tumors, 19 patients with acromegaly, and 95 normal controls. In all patients the monoclonal assay detected a significantly greater number of subjects with elevated a-subunit levels than did the polyclonal assay (21 us. 14; P < 0.01). Fourteen of the 63 patients with clinically nonfunctioning tumors (22%) had elevated serum a-subunit levels in the monoclonal assay vs. 11
(17%) in the polyclonal assay. Among the 19 patients with acromegaly, the prevalence was 7 (37%) and 3 (16%) using the monoclonal and polyclonal assays, respectively.Twenty-eight (44%) of the patients with clinically nonfunctioning pituitary adenomas were female. Eleven (39%) of the women were under 45 yr old, as were 10 (29%) of the men. We conclude that the prevalence of free a-subunit hypersecretion in patients with clinically nonfunctioning and somatotroph adenomas may be higher than previously recognized, and that a sensitive and specific monoclonal antibody free a-subunit assay may provide a useful tumor marker in these patients. The prevalence of clinically nonfunctioning pituitary tumors among younger men and women may also have been previously underestimated. (J Clin Endocrinol Metab 70: 859-864, 1990)
T
HE MAJORITY of pituitary adenomas produce clinical syndromes resulting from the direct effects of hormone hypersecretion by the tumor. However, 2530% of pituitary tumors produce no such syndrome and have been termed clinically nonfunctioning. Recently, it has been reported that a substantial number of clinically nonfunctioning pituitary tumors may synthesize and secrete intact glycoprotein hormones or their free subunits (1-3). This has been shown by a number of in vitro techniques, including cell culture (4-7), analysis of specific RNA species (8-10), and immunocytochemistry (11-13) of surgically excised tumor tissue. Elevated levels of glycoprotein hormones or subunits in the serum of patients with clinically nonfunctioning pituitary tumors has been described (3), but the prevalence of such elevation has not been precisely determined. The presence of such tumor markers is extremely useful for both diagnosis and follow-up. Despite such secretion by these tumors, they are justifiably referred to as clinically non-
functioning because a characteristic clinical syndrome resulting from tumoral hypersecretion has not been identified. Many such patients are found to have mild hyperprolactinemia, which results from pituitary stalk compression and presumed decreased hypothalamic dopaminergic inhibition of PRL secretion. This is confirmed by disproportionately mild hyperprolactinemia relative to tumor size and the absence of immunocytochemically detectible PRL in excised tumor tissue. The pituitary glycoprotein hormones LH, FSH, and TSH are dimeric proteins composed of a common asubunit and a specific /?-subunit. Free a-subunit is detectable in the serum of normal individuals (14, 15) and is secreted by both pituitary thyrotrophs and gonadotrophs (16). a-Subunit levels are elevated in states of increased TSH or gonadotropin secretion, such as in primary hypothyroidism (17) or the menopause (18), and may increase with the administration of GnRH and TRH (19). In addition, ectopic production of free a-subunit by nonpituitary neoplasms has been demonstrated (20, 21). An important advance in the understanding of glycoprotein hormone production in neoplastic tissue has been the finding of elevated serum levels of free a-subunit in patients with pituitary tumors secreting gonadotropins,
Received June 13,1989. Address requests for reprints to: Anne Klibanski, M.D., Massachusetts General Hospital, Boston, Massachusetts 02114. * This work was supported in part by NIH Grants DK-40947, RR01066, and DK-07028.
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OPPENHEIM ET AL.
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TSH, and, rarely, ACTH or PRL (4, 9, 22-30). A subset of patients with acromegaly have been found to cosecrete free a-subunit and GH (28, 30), but the frequency of this cosecretion and its clinical significance have not been determined. In addition, in a subset of pituitary tumors, elevation of serum free a-subunit levels occurs without hypersecretion of other pituitary hormones (24, 31, 32). Free a-subunit has proved useful as a tumor marker in patients with clinically nonfunctioning pituitary tumors. Surgical resection (22, 31) and external radiation (28) of a-subunit-secreting pituitary adenomas have been shown to decrease serum a-subunit levels, and subsequent increases in these levels may indicate tumor growth or recurrence. The measurement of serum asubunit levels may also have importance as an indication of tumor response to medical therapy (33), such as with analogs of dopamine (29) or somatostatin (34). Previous studies of a-subunit secretion have used polyclonal antibodies raised against purified a-subunit. Such antibodies show variable levels of cross-reactivity with intact LH, FSH, and TSH (15, 17, 35, 36). Thus, in states of elevated glycoprotein hormone secretion, it may be difficult to distinguish a-subunit immunoreactivity due to cross-reactivity from that due to abnormal asubunit hypersecretion. Thotakura and Bahl (37) have described a monoclonal antibody that is highly sensitive and specific for uncombined a-subunit. The application of an assay using such an antibody could eliminate many of the problems of intact glycoprotein hormone cross-reactivity and allow several questions to be addressed. 1) What is the prevalence of free asubunit secretion by clinically nonfunctioning pituitary adenomas? 2) Does monoclonal a-subunit immunoreactivity represent a more sensitive tumor marker? 3) Can this assay more readily differentiate abnormal from normal states of a-subunit hypersecretion? 4) What is the prevelence of a-subunit cosecretion in acromegaly? 5) Does such cosecretion affect the natural history of the disease or the response to therapy? We studied two groups of patients with pituitary tumors: a group with clinically nonfunctioning adenomas and a group with somatotroph adenomas. Using the newly developed monoclonal anti-a-subunit antibody assay, we compared these two groups of pituitary tumor patients to normal men, premenopausal women, and postmenopausal women. Materials and Methods Hormone assays Polyclonal a-subunit RIAs were performed as previously described (14). The detection limit for a-subunit is 0.2 ng/tube, with cross-reactivities of 2.5-3.0% with purified intact LH and FSH. Monoclonal a-subunit RIAs were performed using a kit
JCE & M • 1990 Vol70«No4
(Biomerica, Inc., Newport Beach, CA), using a purified monoclonal anti-a-subunit antibody (37). The detection limit for asubunit is 0.05 ng/tube. The cross-reactivities with intact glycoprotein hormones are all less than 0.2%, and those with purified subunits of human LH, FSH, and TSH are less than 0.1%. LH, FSH, and TSH immunoradiometric assays were perfomed using kits from Celltech Diagnostics Ltd. (Slough, Berkshire, United Kingdom). The cross-reactivities of free asubunit in the LH and FSH assays are 0.13% and 0.03%, respectively. Statistical methods Analysis of variance was used to compare the mean a-subunit levels among various groups. Dunnett's test was used to compare the mean a-subunit level of the patients to that of the controls. Macnamar's test was used to compare the number of patients with elevated a-subunit levels detected with the monoclonal and polyclonal a-subunit assays. Study subjects We studied 63 patients with clinically nonfunctioning pituitary adenomas and 19 patients with acromegaly, and compared these patients with 95 normal controls. The patients with clinically nonfunctioning pituitary adenomas represented sequential patients undergoing transsphenoidal pituitary surgery at the Massachusetts General Hospital. Immunocytochemical staining for PRL and GH was negative in all cases. There were 35 male and 28 female patients. None had clinical evidence of acromegaly or Cushing's syndrome, and all had a pathologically confirmed diagnosis of pituitary adenoma at surgery. The age range of the male patients was 24-74 yr (mean ± SD, 52.0 ± 13.1 yr), and that of the female patients was 16-81 yr (mean, 52.2 ± 17.1 yr). Ten of the 35 male patients (29%) were less than 45 yr old. The female patients were divided into 3 groups for analysis: less than 45 yr old (premenopausal age range), greater than 50 yr old with serum FSH and/or LH levels in the normal postmenopausal range (>30 IU/L), and greater than 50 yr old with serum gonadotropin levels below the postmenopausal range. (There were no female patients 45-50 yr old.) This was done to allow comparison of a-subunit levels with those of the appropriate control group; because free a-subunit is cosecreted with gonadotropins and, therefore, may be elevated in postmenopausal women, we compared the a-subunit levels of the older pituitary tumor patients who had elevated gonadotropin levels with those of the postmenopausal control women, and we compared the a-subunit levels of the older pituitary tumor patients who had inappropriately low gonadotropin levels (30 IU/L), 47-73 yr old (mean, 55.2 ± 6.3 yr). The premenopausal women were studied during 3 phases of the menstrual cycle: 8 in the early follicular phase, 10 in the preovulatory phase, and 10 in the luteal phase. All women had a history of normal menstual cycles, and ovulation was confirmed by basal body temperature recording and luteal phase serum progesterone concentrations above 16 nmol/L (>5 ng/mL). None of the controls had any medical illness, and none was taking medication. The mean LH and FSH levels in the control men were 5.0 ± 2.4 and 4.0 ± 3.8 IU/L, respectively.
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TABLE 2. Clinical features of 28 women with clinically nonfunctioning pituitary adenomas No. (%) Age: Gonadotropins:0
50yr
' High gonadotropins = serum LH and/or FSH levels above 30 IU/ L. 6
On formal neuroophthalmological examination. Greater than 10 mm on computed tomographic or magnetic resonance imaging scanning. c
Results Clinical presentation Table 1 summarizes the clinical features of the male study patients. Serum PRL was mildly elevated in 26 of the 35 male nonfunctioning tumor patients (74%) and was greater than 20 ng/L in only 6 (17%). One male patient had evidence of cryptic hypercortisolism (positive ACTH immunocytochemistry and elevated serum cortisol levels without clinical evidence of Cushing's syndrome). None of the men with clinically nonfunctioning pituitary tumors had elevated serum LH levels, and 5 had elevation of serum FSH concentrations. Eleven of the 28 female patients (39%) with clinically nonfunctioning tumors (Table 2) were under 45 yr old. Two had regular menstrual periods, 6 had oligmenorrhea, and 3 were amenorrheic. All 11 of the younger female TABLE 1. Clinical features of 35 men with clinically nonfunctioning pituitary adenomas No. (%) Headache Hypogonadism0 Visual field defect6 Hyperprolactinemia Central hypothyroidism at presentation Central hypoadrenalism at presentation Pituitary apoplexy at presentation Incidental finding Macroadenomac 0
16 (46) 27 (77) 29 (83) 26 (74) 9(26) 10 (29) 3(9) 2(6) 35 (100)
Decreased sexual function and serum testosterone below 10.4 nmol/ L (300 ng/dL). 6 On formal neuroophthalmological examination. e Greater than 10 mm on computed tomographic or magnetic resonance imaging scanning.
patients had mild hyperprolactinemia (>20 /ng/L), and 6 had galactorrhea. Of the 17 women over 50 yr old with clinically nonfunctioning pituitary tumors (Table 2), 7 were found to have the expected elevation of serum LH and FSH (>30 IU/L), but the other 10 had gonadotropin levels below the normal postmenopausal range. Sixteen patients were amenorrheic, and 1 had oligomenorrhea and intermittently elevated gonadotropin levels suggestive of the perimenopause. There were 11 patients with mild hyperprolactinemia, but none had galactorrhea. One woman and three men had tumoral hypersecretion of TSH (with serum TSH levels of 5.3, 5.9, 6.9, and 9.6 mU/L) and positive TSH/5 immunocytochemistry, but were clinically and biochemically euthyroid. a-Subunit levels Table 3 shows the a-subunit levels measured with both the monoclonal antibody and the polyclonal antibody in patients and controls. There was no statistically significant difference between the mean a-subunit concentrations, measured with either the monoclonal or the polyclonal antibody, of any patient group and those of the relevant control group. When the 28 premenopausal control women were subdivided on the basis of the phase of the menstrual cycle, there was no difference in the mean a-subunit levels, measured with either antibody, among these 3 groups (data not shown). Among the normal controls, the postmenopausal women had significantly higher a-subunit levels in both assays than the men and the premenopausal women.
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OPPENHEIM ET AL.
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TABLE 3. Serum a-subunit levels in 82 patients with pituitary adenomas and 95 controls using monoclonal and polyclonal antibodies Monoclonal (ng/L)
Polyclonal (ng/L)
n
Range
Mean
SD
35 11
60-20,000 90-3,700
1,010
3,360 1,050
Range
Mean
SD
300-52,700 590-14,200
3,110 2,170
9,010 4,010
400-1,700 1,400-17,700
1,010 4,200
5,980
700-26,700 540-2,300
4,040 1,130
8,510 2,220 2,830
Nonfunctioning tumors (n = 63) Men
Women 50 yr Low gonadotropins High gonadotropins" Acromegaly (n = 19) Men Women 50 yr Low gonadotropins High gonadotropins Control
10 7
100-3,700 270-8,500
9 6
120-10,000 70-630
2 2
120-1,100 610-2,700
Men
35
Premenopausal women Postmenopausal women
28
70-450 50-460 290-1,500
1
32
580 300
150
1,680
3,010
1,360
3,240
290
210
610
690 1,480
560-3,700 3,300-7,300
2,130 5,300
300-1,700 420-1,600 1,200-7,100
790
300
870
350
3,380
1,640
1,660 190
90
220
110
820
380
440
700
High gonadotropins = serum LH and/or FSH levels above 30 IU/L.
TABLE 4. Number of patients with pituitary tumors and elevated serum a-subunit concentration No. (%) Nonfunctioning tumors Men Women 50 yr Low gonadotropins High gonadotropins0 Total Acromegalics Men
Women 50 yr Low gonadotropins High gonadotropins Total All patients
Monoclonal
Polyclonal
11
9(26) 2(18)
6(17) 2(18)
10 7 63
2 (20) 1(14) 14 (22)
2(20) 1(14) 11(17)
9 6
4(44) 1(17)
2(22) 0(0)
2 2 19
1(50) 1(50) 7(37)
0(0) 1(50) 3(16)
82
21 (26)
14 (17)
35
Elevated serum a-subunit concentration = greater than 2 SD above the mean control concentration. 0 High gonadotropins = serum LH and/or FSH greater than 30 IU/ L.
Table 4 shows the number of pituitary tumor patients in each clinical group who had serum a-subunit levels greater than 2 SD above the mean of the appropriate control group. In the pituitary tumor patients, the monoclonal antibody assay detected a significantly greater number of patients with serum a-subunit elevation than did the polyclonal antibody assay (P < 0.01). Fourteen of the 63 patients with clinically nonfunctioning adenomas (22%) had elevated serum levels of free a-subunit using the monoclonal antibody assay, 3 more than were found using the polyclonal assay (17%). All 3 of these
patients were male. Among the 19 acromegalic patients, 7 (37%) had elevated serum a-subunit levels using the monoclonal assay, whereas 4 had such elevations using the polyclonal assay (21%). All 3 of the acromegalic patients with TSH cosecretion had serum a-subunit elevations in the monoclonal antibody assay. In all, the monoclonal a-subunit assay detected 7 more patients with elevated serum a-subunit levels than did the polyclonal assay.
Discussion We have studied the prevalence of a-subunit hypersecretion in 63 unselected patients with clinically nonfunctioning pituitary adenomas and 19 patients with acromegaly. We have show that, using a highly specific monoclonal anti-a-subunit antibody assay, a significantly greater number of pituitary tumor patients had asubunit hypersecretion (P < 0.01). Twenty-two percent of patients with clinically nonfunctioning pituitary adenomas have elevated serum levels of free a-subunit in the monoclonal a-subunit assay. The monoclonal assay was more sensitive than the polyclonal assay, detecting an additional 3 patients (9%) with a-subunit hypersecretion. a-Subunit hypersecretion was even more prevalent in acromegalic patients (37%), with 4 more patients (21%) being detected in the monoclonal assay than in the polyclonal assay. The prevalence of a-subunit hypersecretion in patients with clinically nonfunctioning pituitary adenomas is not well established. Most other reports have suggested a low frequency of such hypersecretion (11, 22, 24, 28, 30). However, Snyder (3) found that of 139 consecutive male patients with pituitary adenomas, 53 were nonsecreting,
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a-SUBUNIT SECRETION IN PITUITARY TUMORS 8 secreted a-subunit only, and 11 of the 23 FSH-secreting tumors cosecreted free a-subunit. This yields a prevalence of a-subunit hypersecretion in patients with clinically nonfunctioning pituitary tumors of 23%, a result similar to ours. Fourteen percent of our male patients with clinically nonfunctioning pituitary tumors had FSH hypersecretion compared with 17% in Snyder's series (3). a-Subunit cosecretion by somatotroph adenomas has been described (28, 30, 38), but its prevalence is not known. MacFarlane et al. (28) found serum a-subunit elevation in 13 of 46 acromegalic patients (28%), BeckPeccoz et al. (38) found such elevation in 4 of 22 acromegalic patients (18%), and Ishibashi et al. (30) in 5 of 58 (9%). Other reports are primarily case reports (29, 34) rather than large series. These frequencies are lower than our result of 37% using a monoclonal antibody assay and suggest that a monoclonal assay is a more sensitive method of detecting a-subunit hypersecretion in patients with acromegaly as well as in clinically nonfunctioning tumors. There is evidence that GH and a-subunit may coexist within the same tumor cells and, in some cases, within the same secretory granules in patients with acromegaly and a-subunit hypersecretion (39). Two additional findings in our series were the number of patients in the younger age group and the number of female patients. Nearly half (44%) of our unselected patients were women, 39% of whom were under 45 yr old, the youngest being 16 yr old. Furthermore, 40% of the men with clinically nonfunctioning pituitary tumors were under the age of 50 yr, the youngest of whom was 24 yr old. These results differ from most previously reported series, in which the majority of such tumors have been found in men over 40 yr old (2, 3, 24, 40, 41). The diagnosis of these tumors may be more difficult in the older female population because of the absence of an early clinical marker such as oligoamenorrhea and because of the normal elevation of serum gonadotropin levels found after menopause. We conclude that a-subunit hypersecretion may be more common than previously recognized among patients with clinically nonfunctioning pituitary tumors or acromegaly. The sensitive and specific monoclonal asubunit assay may prove to be a useful tool in providing a tumor marker in a significant number of patients with these tumors and may allow for more precise diagnosis, characterization, and follow-up. The biological and clinical significance of a-subunit cosecretion in patients with pituitary tumors is not known at this time. Whether such cosecretion is of importance in the pathogenesis of these tumors or whether it alters the clinical course or response to therapy deserves further study.
863
References 1. Klibanski A. Nonsecreting pituitary tumors. Endocrinol Metab Clin North Am. 1987;16(Suppl 3):793-804. 2. Snyder PJ. Gonadotroph cell pituitary adenomas. Endocrinol Metab Clin North Am. 1987;16(Suppl 3):755-64. 3. Snyder PJ. Gonadotroph adenomas of the pituitary. Endocr Rev. 1985;6:552-63. 4. Mashiter K, Adams E, Van Noorden S. Secretion of LH, FSH and prolactin shown by cell culture and immunocytochemistry of human functionless pituitary adenomas. Clin Endocrinol (Oxf). 1981;15:103-12. 5. Asa SL, Gerrie BM, Singer W, et al. Gonadotropin secretion in vitro by human pituitary null cell adenomas and oncocytomas. J Clin Endocrinol Metab. l986;62:1011-9. 6. Beitins IZ, Lipson LG, McArthur JW. Immunoreactive LH, FSH and their subunits in tissue culture media from normal and adenomatous, human pituitary fragments. J Clin Endocrinol Metab. 1977;45:1271-80. 7. Snyder PJ, Hildegarde MB, Phillips JL, et al. Comparison of the hormonal secretory behavior of gonadotroph cell adenomas in vivo and in culture. Clin Endocrinol Metab. 1985;61:1061-5. 8. Jameson JL, Klibanski A, Black PM, et al. Glycoprotein hormone genes are expressed in clinically non-functioning pituitary adenomas. J Clin Invest. 1987;80:1472-8. 9. Klibanski A, Deutsch PJ, Jameson JL, et al. Luteinizing hormonesecreting pituitary tumor: biosynthetic characterization and clinical studies. J Clin Endocrinol Metab. 1987;64:536-42. 10. Klibanski A, Shupnik MA, Bikkal HA, et al. Dopaminergic regulation of a-subunit secretion and mRNA levels in a-secreting pituitary tumors. J Clin Endocrinol Metab. 1988;66:96-102. 11. Black PM, Hsu DW, Klibanski A, et al. Hormone production in clinically nonfunctioning pituitary adenomas. J Neurosurg. 1987;66:244-50. 12. Kovacs K, Horvath E, Ryan N, et al. Null cell adenoma of the pituitary. Virchows Arch Pathol Histol. 1980;387:165-74. 13. Landolt AM, Heitz PU. Alpha-subunit-producing pituitary adenomas: immunocytochemical and ultrastructural studies. Virchows Arch Pathol Anat. 1986;409:417-31. 14. Kourides IA, Weintraub BD, Levko MA, Maloof F. Alpha and beta subunits of human thyrotropin: purification and development of specific radioimmunoassay. Endocrinology. 1974;94:1411-21. 15. Papapetrou PD. Circulating a-subunit of glycoprotein hormones in normal subjects and its relationship to the LH and FSH serum levels. Acta Endocrinol (Copenh). 1982;(Suppl) 248:1-2. 16. Kourides IA, Weintraub BD, Re RN, Ridgway EC, Maloof F. Thyroid hormone, oestrogen, and glucocorticoid effects on two different pituitary glycoprotein hormone alpha subunit pools. Clin Endocrinol (Oxf). 1978;9:535-42. 17. Kourides IA, Weintraub BD, Ridgway EC, Maloof F. Pituitary secretion of free alpha and beta subunit of human thyrotropin in patients with thyroid disorders. J Clin Endocrinol Metab. 1975;40:872-85. 18. Laburthe MC, Dolais JR, Rosselin GE. Evidence for circulating a subunits of pituitary gonadotropins in plasma. J Clin Endocrinol Metab. 1973;37:156-9. 19. Hagen C, McNeilly AS. Changes in circulating levels of LH, FSH, LH/3- and a-subunit after gonadotropin-releasing hormone, and of TSH, LH/3- and a-subunit after thyrotropin-releasing hormone. J Clin Endocrinol Metab. 1975;41:466-70. 20. Blackman MR, Weintraub BD, Rosen SW, Kourides IA, Steinwascher K, Gail MH. Human placental and pituitary glycoprotein hormones and their subunits as tumor markers: a quantitative assessment. J Natl Cancer Inst. 1980;65:81-92. 21. Papappetrou PD, Anagnostopoulos NI. A gonadotropin and asubunit suppression test for the assessment of the ectopic production of human chorionic gonadotropin and its subunits after the menopause. J Clin Endocrinol Metab. 1985;60:1187-95. 22. Kourides IA, Weintraub BD, Rosen SW, et al. Secretion of alpha subunit of glycoprotein hormones by pituitary adenomas. J Clin Endocrinol Metab. 1976;43:97-106. 23. Demura R, Jibiki K, Kubo O, et al. The significance of a-subunit
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OPPENHEIM ET AL. as a tumor marker for gonadotropin-producing adenomas. J Clin Endocrinol Metab. 1986;63:564-9. Ridgway EC. Glycoprotein hormone production by pituitary tumors. Prog Endocr Res Ther. 1984;l:343-63. Borges JLC, Ridgway EC, Kovacs K, et al. FSH-secreting pituitary tumor with concomitant elevations of serum alpha-subunit levels. J Clin Endocrinol Metab. 1984;58:937-41. Chapman AJ, MacFarlane IA, Shalet SM, et al. Discordant serum a-subunit and FSH concentrations in a woman with a pituitary tumour. Clin Endocrinol (Oxf). 1984;21:123-9. Snyder PJ, Bashey JM, Kim SU, et al. Secretion of uncombined subunits of LH by gonadotroph cell adenomas. J Clin Endocrinol Metab. 1984;59:1169-75. MacFarlane IA, Beardwell CG, Shalet SM, et al. Glycoprotein hormone alpha-subunit secretion in patients with pituitary adenomas: influence of external irradiation. Clin Endocrinol (Oxf). 1980;13:215-22. MacFarlane IA, Beardwell CG, Shalet SM, et al. Glycoprotein hormone alpha-subunit secretion in patients with pituitary adenomas: influence of TRH, LRH, and bromocriptine. Acta Endocrinol (Copenh). 1982;99:487-92.
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hormone-secreting pituitary tumors. Endocrinol Metab Clin North Am. 1989;18(Suppl 2):339-58. Sassolas G, Serusclat P, Claustrat B, et al. Plasma alpha-subunit levels during the treatment of pituitary adenomas with the somatostatin analogue (SMS 201-995). Horm Res. 1988,29:124-8. Snyder PJ, Johnson J, Muzyka R. Abnormal secretion of glycoprotein alpha-subunit and FSH/3-subunit in men with pituitary adenomas and FSH hypersecretion. J Clin Endocrinol Metab. 1980;51:579-84. Hagen C, McNeilly AS. The specificity and application of radioimmunoassay for the a-subunit of luteinizing hormone in man. Acta Endocrinol (Copenh). 1975;41:466-70. Thotakura NR, Bahl OP. Highly specific and sensitive hybridoma antibodies against the a-subunit of human glycoprotein hormones. Endocrinology. 1985;117:1300-8. Beck-Peccoz P, Bassetti M, Spada A, et al. Glycoprotein hormone a-subunit response to growth hormone (GH)-releasing hormone in patients with active acromegaly. Evidence for a-subunit and GH coexistence in the same tumor cell. J Clin Endocrinol Metab. 1985;61:541-6. Osamura RY, Watanabe K. Immunohistochemical colocalization
30. Ishibashi M, Yamaji T, Takaku F, Teramoto A, Fukushima T.
of growth hormone (GH) and a subunit in human GH secreting
Secretion of glycoprotein hormone a-subunit by pituitary tumors. J Clin Endocrinol Metab. 1987;64:1187-93. 31. Ridgway EC, Klibanski A, Ladenson PW, et al. Pure alpha-secreting pituitary adenomas. N Engl J Med. 1981;304:1254-9. 32. Klibanski A, Ridgway EC, Zervas NT. Pure alpha subunit-secreting pituitary tumors. J Neurosurg. 1983;59:585-9. 33. Oppenheim DS, Klibanski A. Medical therapy of glycoprotein
pituitary adenomas. Vichows Arch Pathol Anat. 1987;411:323-30. 40. Snyder PJ, Bigdeli J, Gardner DF, et al. Gonadal function in fifty men with untreated pituitary adenomas. J Clin Endocrinol Metab. 1979;48:309-14. 41. Ebersold MJ, Quast LM, Laws ER, et al. Long-term results in transsphenodial removal of nonfunctioning pituitary adenomas. J Neurosurg. 1986;64:713-9.
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