High Incidence of Spontaneous Cervical and Vaginal Tumors in an Inbred Strain of Brown Norway Rats (BN/Bi) 1 J. D. Burek, C. Zurcher, and C. F. Hollander2 ,
3
ABSTRACT-The incidence of spontaneously occurring tumors of the cervix and vagina was unusually high in an inbred strain of Brown Norway rats (BN/Bi). Fifty·four tumors were diagnosed in the cervixes or vaginas of 252 rats. Of the tumors, 7 were squa· mous cell carcinomas, 4 were leiomyomas, and the rest were sarcomas. These tumors were found in nearly 20% of all female rats that died naturally.-J Nail Cancer Inst 57: 549-554, 1976.
Spontaneously occurring tumors of the cervix or vagina are rare in rats. Snell (1) and Franks (2) have reviewed the literature on tumors of the reproductive tracts of female rats; only 4 cervical and 9 vaginal tumors were reported. In addition, a vaginal myxoma (3) was described. The rare occurrence of cervical and vaginal tumors was also borne out by Baba and von Haam (4), who recently reviewed the literature on reproductive tract tumors in rats, and by the lack of additional references in (5). However, several hundred benign and malignant tumors of the uterine horns have been documented. While examining 252 female Brown Norway rats (BN/ Bi), we found an unusually high incidence of tumors in the cervix and vagina and have described them here. Other tumors also present in these rats, the age-associated incidences, and tumor metastases are discussed in
were made: 1) the percent of all necropsied animals of a given age group that died bearing cervical or vaginal tumors, and 2) the tumor incidence calculated with the use of life-table techniques (8) giving the percentage of tumor-bearing animals dying during a specific interval versus the animals at risk. According to the second calculation, an apparent increase in tumors occurred with age in these rats. Table 2 summarizes the number of diagnoses of each tumor type, the rats' ages, and the rats with metastases. In 1 rat, a large tumor was observed grossly, but histologic material was not available; therefore, this animal was included in the calculations of table 1 but not in table 2, in which specific diagnoses were gIven. Gross Examination
The gross appearance of the tumors varied; they ranged from a few millimeters to several centimeters in diameter. Generally, it was difficult to determine if the tumor originated in the cervix or vagina. Some tumors were clearly confined to the cervix and others to the vagina. Most were round, nodular, firm growths; however, some were a diffuse or generalized thickening of the cervix, vagina, or both, without discrete nodule formation. Most tumors could be dissected from the surrounding pelvic structures; however, some had extensive local invasion of the colon, abdominal wall, and perineal region. The larger tumors obstructed the colon; inability to pass feces resulted in megacolon rostral to the obstruction. One rat had multiple smaller tumor nodules seeded into the peritoneal cavity. The cut surface of the tumors was white-to-yellow and usually moist and glistening. Ulcerations of the cervical and vaginal mucosal surface, hemorrhage, and necrotic foci in the tumors often occurred. Three tumors were not observed during gross examination.
(6) . MATERIALS AND METHODS
BN/Bi rats, obtained from Microbiological Associates Inc. (Bethesda, Md.) in 1963, have been inbred in Rijswijk since then and are in their 20th generation. The care, housing, and necropsy procedures were described in (7). The rats were born and reared in a closed colony under strict SPF conditions. Retired breeders (=8 mo old) to be used in longevity studies were transferred to a separate building and maintained under clean conventional conditions. Three-month-old SPF virgin rats were transferred to the same colony where they lived out their natural lives and were necropsied when they were found dead or killed when moribund. Only cervical and vaginal tumors were reported. Dead rats that were autolytic or partially eaten were discarded. Tissues were fixed in 4% neutral buffered formalin. After routine processing, the sections were stained with HPS. A minimum of two (usually three or four) sections were taken from each tumor. In addition to the routine HPS stain, we examined selected cases by using one or more of the following special stains: PAS, mucicarmine, alcian blue, Masson's trichrome, or Gomori's reticulum stain.
Histologic Examination
As summarized in table 2, several distinct tumor patterns were observed. The overall problem was more complex because most of the listed sarcomas had areas within the mqjor tumor pattern that showed transition into one or more of the other sarcoma classifications. Most sarcomas were too large and had destroyed too much of the cervix or vagina for a determination of the ABBREVIATIONS USED: SPF=specific-pathogen-free; HPS=hematoxylin-phloxine-saffron; PAS=periodic acid-Schiff. Received November 3, 1975; accepted February 23, 1976. Institute for Experimental Gerontology TNO, 151 Lange Kleiweg, Rijswijk(ZH), The Netherlands. 3 We thank Miss A. 1. Nooteboom for preparing tissue sections and Mr. A Glaudemans for taking the light micrographs. 1
RESULTS
2
The occurrence of tumors in the cervis and vagina according to age is shown in table 1. Two calculations VOL. 57, NO.3, SEPTEMBER 1976
549
J
NATL CANCER INST
BUREK, ZURCHER, AND HOLLANDER
550
TABLE 1. --Occurrence of spontaneous cervical and vaginal tumors in BN/Bi rats of various age groups
Age mo
6-12 13-18 19-24 25-30 31-36 37-54 Total
Number of rats alive at beginning of period
Number of rats that died during period
Number of rats with tumors
Percent of dead rats with tumors·
2 14 29 81 98 28 252
0 2 9 16 18 4 49
0 14.3 31.0 19.4 18.3 14.3 19.4
252 250 236 207 126 28
Percent of tumorbearing rats at risk" 0 0.8 3.8 7.7 14.3 14.3
• Number of rats with tumors x 100. Number of dead rats Number of rats with tumors
" Number of rats alive at beginning of period
x 100 .
TABLE 2. -Classification of cervical and vaginal tumors in 48 female BN/Bi rats
Tumor classification·
Leiomyoma Leiomyosarcoma Round cell sarcoma Diffuse stromal (submucosal) sarcoma Anaplastic sarcoma Squamous cell carcinoma Total number of tumors
Number of rats with the specific tumor
Mean age, in mo (range)
Number of rats with metastases
4 13 22 6
34(27-40) 31(17-37) 26(18-38) 27(24-30)
0 2 1 0
2 7
32(31-34) 29(24-36)
2 1
54
29(17-40)
6
• Based on the most characteristic pattern.
precise area of origin. A few tumors, however, appeared to originate in the outer, smooth muscle wall (fig. 1). Seventeen tumors had characteristics of smooth muscle tumors. They were composed of elongated spindle cells with pink cytoplasm; cell boundaries were distinct, and the nuclei were long and slender with well-rounded ends. Many areas had several cells that lay parallel for several microscopic fields. Four of these tumors were well-differentiated, sharply circumscribed leiomyomas. Thirteen tumors were leiomyosarcomas with numerous mitoses, cellular pleomorphism, and extensive local invasion into or through the outer muscle layers of the cervix or vagina. Two leiomyosarcomas had distant metastases. Several sarcomas also had cells that consisted of round-to-polygonal cells with vacuolated or pink granular cytoplasm (fig. 2), whereas others had a diffuse cell reaction of the cervix and/or vaginal submucosa that appeared to blend into a diffuse, proliferative stromal sarcoma. The cells in these areas were pleomorphic and usually had indistinct cell boundaries, vacuolated cytoplasm, and round nuclei. Mitoses were frequent and
J NATL CANCER INST
many were atypical. Occasionally, multinucleated giant cells were present. We classified 22 tumors as round cell sarcomas; however, their unusual pattern made them impossible to classify with certainty. Most cells were round-to-polygonal and arranged compactly. Many had indistinct cell boundaries and an epithelioid appearance with pale pink (fig. 3) or vacuolated (fig. 4) cytoplasm. The vacuoles were either solitary, multiple, or more diffuse and occupied most of the cytoplasm. These cytoplasmic spaces did not stain with PAS, alcian blue, or mucicarmine. The nuclei were pleomorphic but tended to be round, though in some areas the nuclei and cytoplasm were slightly elongated. Along the edge of one of these tumors, a transition to elongated tumor cells similar to smooth muscle cells had occurred. Even in this area, round cells with clear cytoplasm were detected. Areas suggesting a transition into a diffuse stromal sarcoma were present in several of these tumors. One round-cell tumor metastasized to regional lymph nodes. All round-cell sarcomas were highly vascularized; the vessel walls often consisted of tumor cells with no discernible muscle wall. Cystic spaces were frequent (fig. 5); some were clear vascular channels with blood in the lumen, which was lined by endothelial cells. Other spaces did not contain blood but were bordered by endothelial cells. Finally, most spaces were empty and the tumor cells formed the linings of the cystic spaces. Two tumors were highly anaplastic sarcomas and had pleomorphic cells, numerous bizarre mitoses, and many multinucleated giant cells. Both locally invaded the pelvic region, perineal area, and ventral abdominal wall. One tumor did have areas of clear cytoplasmic round cells described earlier; the other had an accompanying diffuse stromal proliferation similar to that observed in the more differentiated leiomyosarcomas and the round-cell epithelioid tumors. One tumor had widespread metastases to the peritoneal cavity and lungs; the other metastasized extensively to several mesenteric lymph nodes. Six tumors consisted of large masses formed by what appeared to be diffuse sarcoma of the submucosa (fig. 6). Cells were round or slightly spindle shaped but were more loosely arranged; mitoses were numerous. Sometimes bizarre, multinucleated giant cells invaded or extended from the submucosa to the outer muscle wall. Histologically, these were anaplastic tumors, but they were diffuse and not localized. One of the four had areas suggesting a transition to an elongated spindle cell, and one had areas that were identical in pattern to the round-cell sarcoma noted earlier. The others appeared as diffuse or generalized sarcomas of the cervical and vaginal submucosa. Finally, 7 rats had invasive squamous cell carcinomas of the vagina. Two also had large, round-cell sarcomas of the cervix described previously; 3 rats with squamous carcinomas also had diffuse stromal sarcomas separate from the epithelial tumors. The other 2 rats had invasive squamous carcinomas only. Some rats also had areas of atypical hyperplasia of the cervical and vaginal epithelium; these were usually associated with an underlying sarcoma. VOL. 57, NO.3, SEPTEMBER 1976
CERVICAL AND VAGINAL TUMORS IN RATS DISCUSSION
BN/Bi is the first documented rat strain with a high incidence of tumors involving the cervix and vagina. The highly malignant character both by histologic criteria and biologic behavior is also exceptional. Histologically, several tumor patterns were found (table 2). The precise cell of origin for all the tumors cannot be determined with certainty. Seven were clearly squamous cell carcinomas; about one-third of the tumors definitely had a smooth muscle origin, and the rest had an epithelioid or round-cell pattern. Many of these were similar to the descriptions in (9-12) for bizarre (epithelioid) leiomyosarcomas. Others appeared as diffuse stromal sarcomas, which may also be variants of smooth muscle tumors. Most tumors had regions in which one or more patterns could be found 'and zones of transition from one tumor type to another. From this evidence, all the sarcomas reported here are probably variants of smooth muscle tumors. Although spontaneous tumors in rats are rare, several investigators have, by chemical means, induced cervical and vaginal tumors that often resembled those observed here. Among these scientists, Alexandrov (13) induced vaginal leiomyosarcomas in rats after feedings of methylnitrosourea and ethylnitrosourea during their pregnancies. Glucksmann and Cherry (14,15) induced sarcomas by painting the vaginas with 7, 12-dimethylbenz[a]anthracene. As noted in some spontaneous tumors of the BN/Bi rat, the cells in the experimental tumors were anaplastic, with many multinucleated giant cells. The induced vaginal tumors exhibited extensive local invasion of the vaginal wall and pelvic region. We reported similar results for the spontaneous tumors. Rarely did the induced tumors have distant metastases. Five sarcomas and one squamous cell carcinoma in the BN/Bi rat had distant metastases. Since the only reports of numerous malignant tumors in the cervix and vagina were found after chemical induction, we considered the possibility of such a contamination of the BN/Bi rats. No obvious sources of chemical exposure could be found. In addition, like the BN/Bi rats, the inbred WAG/Rij rat strain is also maintained under identical conditions for studies on aging; data on the incidence of spontaneous tumors for W AG/ Rij rats have been reported (16), and only one cervical sarcoma was found in 290 females examined. Unfortunately, the initial record system did not permit the obtaining of data on the number of pregnancies or virgins. Of the 252 rats reported here, some are retired breeders but most are virgins. How many, if any, of the retired breeders developed tumors could not be
VOL. 57, NO.3, SEPTEMBER 1976
551
determined; however, of 20 virgin rats examined, 4 (20%) had cervical or vaginal tumors. The BN/Bi rat may be a useful model for the study of cervical and vaginal tumors and especially smooth muscle sarcomas. It may also be useful as a source of rats in which to test carcinogens that induce vaginal and cervical tumors and to compare results with rat strains known to have low incidence of those tumors. The location of the tumors makes it possible to observe them before the animals die or are killed. Because the incidence is about 20% in females over 2 years of age, sufficient numbers of rats could be produced to provide a useful source for these unusual tumors. REFERENCES
(1) SNELL KC: Spontaneous lesions of the rat. In The Pathology of Laboratory Animals (Ribelin WE, McCoy JR, eds.). Springfield, Ill., Thomas, 1965, pp 270-273 (2) FRANKS LM: Normal and pathological anatomy and histology of the genital tract of rats and mice. In Pathology of Laboratory Rats and Mice (Cotchin E, Roe FJ, eds.). Oxford, England, Blackwell, 1967, pp 483-489 (3) KLEIN-SZANTO AJ, CONTI CJ, CARTAGE NOVA RE: Ultrastructure ofa vaginal myxoma ofa rat. Vet Patholll:289-296, 1974 (4) BABA N, VON HAAM E: Tumors of the vagina, uterus, placenta and oviduct. In Pathology of Tumors in Laboratory Animals (Turusov VS, ed.), vol I, part 2. Scientific Publication No.6. Lyon, International Agency for Research on Cancer, 1976. In press (5) ROBINSON FR, BROWN RJ, CASEY HW: References on naturally occurring neoplasms in animals. In Registry of Veterinary Pathology, Washington, D.C., Armed Forces Inst Pathol, 1974, pp 103-107 (6) BUREK ]D, HOLLANDER CF: Incidence patterns of tumors in BN/ Bi rats.] Natl Cancer Inst. In press (7) HOLLANDER CF: Current experience using the laboratory rat in aging studies. Lab Anim Sci 26:320-328, 1976 (8) SACHS R: Life table technique in the analysis of response-time data from laboratory experiments on animals. Toxicol Appl Pharmacol 1:203-227, 1959 (9) STOUT AP: Bizarre smooth muscle tumors of the stomach. Cancer 15:400-409, 1962 (10) STOUT AP, LATTES R: Tumors of the soft tissues. In Atlas of Tumor Pathology, Washington, D.C., Armed Forces Inst Pathol, fasc I, ser 2,1967, pp 58-63 (11) MARTlN]F, BAZIN P, FEROLDI], et al: Tumeurs myoides intramurales de I'estomac. Considerations microscopiques a propos de 6 cas. Ann Anat Pathol (Paris) 5:484-497, 1960 (12) ENZINGER FM: Histological typing of soft tissue tumors. In International Histological Classification of Tumors, No.3. Geneva, WHO, 1969, P 31 (13) ALEXANDROV VA: Uterine and mammary tumours induced by nitrosoureas in pregnant rats. Nature 222: 1064-1065, 1969 (14) CHERRY CP, GLUCKSMANN A: The induction of cervico-vaginal tumours in oestrogenized and androgenized rats. Br] Cancer 22:728-742, 1968 (15) GLUCKSMANN A, CHERRY CP: The effect of oestrogens, testosterone and progesterone in the induction of cervico-vaginal tumours in intact and castrate rats. Br] Cancer 22:545-562, 1968 (16) BOORMAN GA, HOLLANDER CF: Spontaneous lesions in the female WAG/Rij (Wistar) rat.] GerontoI28:152-159, 1973
] NATL CANCER INST
FIGURE
I.-Cross section of cervix of 23-month-old BN/Bi rat, with small round cell sarcoma arising in outer muscle wall. x
18
2.-Area within leiomyosarcoma showing transitions between elongated and round tumor cells. Most tumor cells have vacuolated or finely granular pink cytoplasm. x 500
FIGURE
552
BUREK, ZURCHER, AND HOLLANDER
3.-Round-cell sarcoma with area of slightly elongated cells having oval nuclei and variable amounts of pink cytoplasm. x 500 FIGURE 4.-Round-cell sarcoma with nearly all tumor cells showing vacuolated cytoplasm. Note bizarre giant cell. x 500 FIGURE
BUREK, ZURCHER, AND HOLLANDER
553
5.-Round cell sarcoma of vagina, with cystic spaces and infiltration into colon wall. x 18 FIGURE 6.-Diffuse stromal (submucosal) sarcoma of cervix. Tumor cells extend from ulcerated mucosal surface (M) into outer smooth muscle wall (SM). x 80 FIGURE
554
BUREK, ZURCHER, AND HOLLANDER.
3
ABSTRACT-The incidence of spontaneously occurring tumors of the cervix and vagina was unusually high in an inbred strain of Brown Norway rats (BN/Bi). Fifty·four tumors were diagnosed in the cervixes or vaginas of 252 rats. Of the tumors, 7 were squa· mous cell carcinomas, 4 were leiomyomas, and the rest were sarcomas. These tumors were found in nearly 20% of all female rats that died naturally.-J Nail Cancer Inst 57: 549-554, 1976.
Spontaneously occurring tumors of the cervix or vagina are rare in rats. Snell (1) and Franks (2) have reviewed the literature on tumors of the reproductive tracts of female rats; only 4 cervical and 9 vaginal tumors were reported. In addition, a vaginal myxoma (3) was described. The rare occurrence of cervical and vaginal tumors was also borne out by Baba and von Haam (4), who recently reviewed the literature on reproductive tract tumors in rats, and by the lack of additional references in (5). However, several hundred benign and malignant tumors of the uterine horns have been documented. While examining 252 female Brown Norway rats (BN/ Bi), we found an unusually high incidence of tumors in the cervix and vagina and have described them here. Other tumors also present in these rats, the age-associated incidences, and tumor metastases are discussed in
were made: 1) the percent of all necropsied animals of a given age group that died bearing cervical or vaginal tumors, and 2) the tumor incidence calculated with the use of life-table techniques (8) giving the percentage of tumor-bearing animals dying during a specific interval versus the animals at risk. According to the second calculation, an apparent increase in tumors occurred with age in these rats. Table 2 summarizes the number of diagnoses of each tumor type, the rats' ages, and the rats with metastases. In 1 rat, a large tumor was observed grossly, but histologic material was not available; therefore, this animal was included in the calculations of table 1 but not in table 2, in which specific diagnoses were gIven. Gross Examination
The gross appearance of the tumors varied; they ranged from a few millimeters to several centimeters in diameter. Generally, it was difficult to determine if the tumor originated in the cervix or vagina. Some tumors were clearly confined to the cervix and others to the vagina. Most were round, nodular, firm growths; however, some were a diffuse or generalized thickening of the cervix, vagina, or both, without discrete nodule formation. Most tumors could be dissected from the surrounding pelvic structures; however, some had extensive local invasion of the colon, abdominal wall, and perineal region. The larger tumors obstructed the colon; inability to pass feces resulted in megacolon rostral to the obstruction. One rat had multiple smaller tumor nodules seeded into the peritoneal cavity. The cut surface of the tumors was white-to-yellow and usually moist and glistening. Ulcerations of the cervical and vaginal mucosal surface, hemorrhage, and necrotic foci in the tumors often occurred. Three tumors were not observed during gross examination.
(6) . MATERIALS AND METHODS
BN/Bi rats, obtained from Microbiological Associates Inc. (Bethesda, Md.) in 1963, have been inbred in Rijswijk since then and are in their 20th generation. The care, housing, and necropsy procedures were described in (7). The rats were born and reared in a closed colony under strict SPF conditions. Retired breeders (=8 mo old) to be used in longevity studies were transferred to a separate building and maintained under clean conventional conditions. Three-month-old SPF virgin rats were transferred to the same colony where they lived out their natural lives and were necropsied when they were found dead or killed when moribund. Only cervical and vaginal tumors were reported. Dead rats that were autolytic or partially eaten were discarded. Tissues were fixed in 4% neutral buffered formalin. After routine processing, the sections were stained with HPS. A minimum of two (usually three or four) sections were taken from each tumor. In addition to the routine HPS stain, we examined selected cases by using one or more of the following special stains: PAS, mucicarmine, alcian blue, Masson's trichrome, or Gomori's reticulum stain.
Histologic Examination
As summarized in table 2, several distinct tumor patterns were observed. The overall problem was more complex because most of the listed sarcomas had areas within the mqjor tumor pattern that showed transition into one or more of the other sarcoma classifications. Most sarcomas were too large and had destroyed too much of the cervix or vagina for a determination of the ABBREVIATIONS USED: SPF=specific-pathogen-free; HPS=hematoxylin-phloxine-saffron; PAS=periodic acid-Schiff. Received November 3, 1975; accepted February 23, 1976. Institute for Experimental Gerontology TNO, 151 Lange Kleiweg, Rijswijk(ZH), The Netherlands. 3 We thank Miss A. 1. Nooteboom for preparing tissue sections and Mr. A Glaudemans for taking the light micrographs. 1
RESULTS
2
The occurrence of tumors in the cervis and vagina according to age is shown in table 1. Two calculations VOL. 57, NO.3, SEPTEMBER 1976
549
J
NATL CANCER INST
BUREK, ZURCHER, AND HOLLANDER
550
TABLE 1. --Occurrence of spontaneous cervical and vaginal tumors in BN/Bi rats of various age groups
Age mo
6-12 13-18 19-24 25-30 31-36 37-54 Total
Number of rats alive at beginning of period
Number of rats that died during period
Number of rats with tumors
Percent of dead rats with tumors·
2 14 29 81 98 28 252
0 2 9 16 18 4 49
0 14.3 31.0 19.4 18.3 14.3 19.4
252 250 236 207 126 28
Percent of tumorbearing rats at risk" 0 0.8 3.8 7.7 14.3 14.3
• Number of rats with tumors x 100. Number of dead rats Number of rats with tumors
" Number of rats alive at beginning of period
x 100 .
TABLE 2. -Classification of cervical and vaginal tumors in 48 female BN/Bi rats
Tumor classification·
Leiomyoma Leiomyosarcoma Round cell sarcoma Diffuse stromal (submucosal) sarcoma Anaplastic sarcoma Squamous cell carcinoma Total number of tumors
Number of rats with the specific tumor
Mean age, in mo (range)
Number of rats with metastases
4 13 22 6
34(27-40) 31(17-37) 26(18-38) 27(24-30)
0 2 1 0
2 7
32(31-34) 29(24-36)
2 1
54
29(17-40)
6
• Based on the most characteristic pattern.
precise area of origin. A few tumors, however, appeared to originate in the outer, smooth muscle wall (fig. 1). Seventeen tumors had characteristics of smooth muscle tumors. They were composed of elongated spindle cells with pink cytoplasm; cell boundaries were distinct, and the nuclei were long and slender with well-rounded ends. Many areas had several cells that lay parallel for several microscopic fields. Four of these tumors were well-differentiated, sharply circumscribed leiomyomas. Thirteen tumors were leiomyosarcomas with numerous mitoses, cellular pleomorphism, and extensive local invasion into or through the outer muscle layers of the cervix or vagina. Two leiomyosarcomas had distant metastases. Several sarcomas also had cells that consisted of round-to-polygonal cells with vacuolated or pink granular cytoplasm (fig. 2), whereas others had a diffuse cell reaction of the cervix and/or vaginal submucosa that appeared to blend into a diffuse, proliferative stromal sarcoma. The cells in these areas were pleomorphic and usually had indistinct cell boundaries, vacuolated cytoplasm, and round nuclei. Mitoses were frequent and
J NATL CANCER INST
many were atypical. Occasionally, multinucleated giant cells were present. We classified 22 tumors as round cell sarcomas; however, their unusual pattern made them impossible to classify with certainty. Most cells were round-to-polygonal and arranged compactly. Many had indistinct cell boundaries and an epithelioid appearance with pale pink (fig. 3) or vacuolated (fig. 4) cytoplasm. The vacuoles were either solitary, multiple, or more diffuse and occupied most of the cytoplasm. These cytoplasmic spaces did not stain with PAS, alcian blue, or mucicarmine. The nuclei were pleomorphic but tended to be round, though in some areas the nuclei and cytoplasm were slightly elongated. Along the edge of one of these tumors, a transition to elongated tumor cells similar to smooth muscle cells had occurred. Even in this area, round cells with clear cytoplasm were detected. Areas suggesting a transition into a diffuse stromal sarcoma were present in several of these tumors. One round-cell tumor metastasized to regional lymph nodes. All round-cell sarcomas were highly vascularized; the vessel walls often consisted of tumor cells with no discernible muscle wall. Cystic spaces were frequent (fig. 5); some were clear vascular channels with blood in the lumen, which was lined by endothelial cells. Other spaces did not contain blood but were bordered by endothelial cells. Finally, most spaces were empty and the tumor cells formed the linings of the cystic spaces. Two tumors were highly anaplastic sarcomas and had pleomorphic cells, numerous bizarre mitoses, and many multinucleated giant cells. Both locally invaded the pelvic region, perineal area, and ventral abdominal wall. One tumor did have areas of clear cytoplasmic round cells described earlier; the other had an accompanying diffuse stromal proliferation similar to that observed in the more differentiated leiomyosarcomas and the round-cell epithelioid tumors. One tumor had widespread metastases to the peritoneal cavity and lungs; the other metastasized extensively to several mesenteric lymph nodes. Six tumors consisted of large masses formed by what appeared to be diffuse sarcoma of the submucosa (fig. 6). Cells were round or slightly spindle shaped but were more loosely arranged; mitoses were numerous. Sometimes bizarre, multinucleated giant cells invaded or extended from the submucosa to the outer muscle wall. Histologically, these were anaplastic tumors, but they were diffuse and not localized. One of the four had areas suggesting a transition to an elongated spindle cell, and one had areas that were identical in pattern to the round-cell sarcoma noted earlier. The others appeared as diffuse or generalized sarcomas of the cervical and vaginal submucosa. Finally, 7 rats had invasive squamous cell carcinomas of the vagina. Two also had large, round-cell sarcomas of the cervix described previously; 3 rats with squamous carcinomas also had diffuse stromal sarcomas separate from the epithelial tumors. The other 2 rats had invasive squamous carcinomas only. Some rats also had areas of atypical hyperplasia of the cervical and vaginal epithelium; these were usually associated with an underlying sarcoma. VOL. 57, NO.3, SEPTEMBER 1976
CERVICAL AND VAGINAL TUMORS IN RATS DISCUSSION
BN/Bi is the first documented rat strain with a high incidence of tumors involving the cervix and vagina. The highly malignant character both by histologic criteria and biologic behavior is also exceptional. Histologically, several tumor patterns were found (table 2). The precise cell of origin for all the tumors cannot be determined with certainty. Seven were clearly squamous cell carcinomas; about one-third of the tumors definitely had a smooth muscle origin, and the rest had an epithelioid or round-cell pattern. Many of these were similar to the descriptions in (9-12) for bizarre (epithelioid) leiomyosarcomas. Others appeared as diffuse stromal sarcomas, which may also be variants of smooth muscle tumors. Most tumors had regions in which one or more patterns could be found 'and zones of transition from one tumor type to another. From this evidence, all the sarcomas reported here are probably variants of smooth muscle tumors. Although spontaneous tumors in rats are rare, several investigators have, by chemical means, induced cervical and vaginal tumors that often resembled those observed here. Among these scientists, Alexandrov (13) induced vaginal leiomyosarcomas in rats after feedings of methylnitrosourea and ethylnitrosourea during their pregnancies. Glucksmann and Cherry (14,15) induced sarcomas by painting the vaginas with 7, 12-dimethylbenz[a]anthracene. As noted in some spontaneous tumors of the BN/Bi rat, the cells in the experimental tumors were anaplastic, with many multinucleated giant cells. The induced vaginal tumors exhibited extensive local invasion of the vaginal wall and pelvic region. We reported similar results for the spontaneous tumors. Rarely did the induced tumors have distant metastases. Five sarcomas and one squamous cell carcinoma in the BN/Bi rat had distant metastases. Since the only reports of numerous malignant tumors in the cervix and vagina were found after chemical induction, we considered the possibility of such a contamination of the BN/Bi rats. No obvious sources of chemical exposure could be found. In addition, like the BN/Bi rats, the inbred WAG/Rij rat strain is also maintained under identical conditions for studies on aging; data on the incidence of spontaneous tumors for W AG/ Rij rats have been reported (16), and only one cervical sarcoma was found in 290 females examined. Unfortunately, the initial record system did not permit the obtaining of data on the number of pregnancies or virgins. Of the 252 rats reported here, some are retired breeders but most are virgins. How many, if any, of the retired breeders developed tumors could not be
VOL. 57, NO.3, SEPTEMBER 1976
551
determined; however, of 20 virgin rats examined, 4 (20%) had cervical or vaginal tumors. The BN/Bi rat may be a useful model for the study of cervical and vaginal tumors and especially smooth muscle sarcomas. It may also be useful as a source of rats in which to test carcinogens that induce vaginal and cervical tumors and to compare results with rat strains known to have low incidence of those tumors. The location of the tumors makes it possible to observe them before the animals die or are killed. Because the incidence is about 20% in females over 2 years of age, sufficient numbers of rats could be produced to provide a useful source for these unusual tumors. REFERENCES
(1) SNELL KC: Spontaneous lesions of the rat. In The Pathology of Laboratory Animals (Ribelin WE, McCoy JR, eds.). Springfield, Ill., Thomas, 1965, pp 270-273 (2) FRANKS LM: Normal and pathological anatomy and histology of the genital tract of rats and mice. In Pathology of Laboratory Rats and Mice (Cotchin E, Roe FJ, eds.). Oxford, England, Blackwell, 1967, pp 483-489 (3) KLEIN-SZANTO AJ, CONTI CJ, CARTAGE NOVA RE: Ultrastructure ofa vaginal myxoma ofa rat. Vet Patholll:289-296, 1974 (4) BABA N, VON HAAM E: Tumors of the vagina, uterus, placenta and oviduct. In Pathology of Tumors in Laboratory Animals (Turusov VS, ed.), vol I, part 2. Scientific Publication No.6. Lyon, International Agency for Research on Cancer, 1976. In press (5) ROBINSON FR, BROWN RJ, CASEY HW: References on naturally occurring neoplasms in animals. In Registry of Veterinary Pathology, Washington, D.C., Armed Forces Inst Pathol, 1974, pp 103-107 (6) BUREK ]D, HOLLANDER CF: Incidence patterns of tumors in BN/ Bi rats.] Natl Cancer Inst. In press (7) HOLLANDER CF: Current experience using the laboratory rat in aging studies. Lab Anim Sci 26:320-328, 1976 (8) SACHS R: Life table technique in the analysis of response-time data from laboratory experiments on animals. Toxicol Appl Pharmacol 1:203-227, 1959 (9) STOUT AP: Bizarre smooth muscle tumors of the stomach. Cancer 15:400-409, 1962 (10) STOUT AP, LATTES R: Tumors of the soft tissues. In Atlas of Tumor Pathology, Washington, D.C., Armed Forces Inst Pathol, fasc I, ser 2,1967, pp 58-63 (11) MARTlN]F, BAZIN P, FEROLDI], et al: Tumeurs myoides intramurales de I'estomac. Considerations microscopiques a propos de 6 cas. Ann Anat Pathol (Paris) 5:484-497, 1960 (12) ENZINGER FM: Histological typing of soft tissue tumors. In International Histological Classification of Tumors, No.3. Geneva, WHO, 1969, P 31 (13) ALEXANDROV VA: Uterine and mammary tumours induced by nitrosoureas in pregnant rats. Nature 222: 1064-1065, 1969 (14) CHERRY CP, GLUCKSMANN A: The induction of cervico-vaginal tumours in oestrogenized and androgenized rats. Br] Cancer 22:728-742, 1968 (15) GLUCKSMANN A, CHERRY CP: The effect of oestrogens, testosterone and progesterone in the induction of cervico-vaginal tumours in intact and castrate rats. Br] Cancer 22:545-562, 1968 (16) BOORMAN GA, HOLLANDER CF: Spontaneous lesions in the female WAG/Rij (Wistar) rat.] GerontoI28:152-159, 1973
] NATL CANCER INST
FIGURE
I.-Cross section of cervix of 23-month-old BN/Bi rat, with small round cell sarcoma arising in outer muscle wall. x
18
2.-Area within leiomyosarcoma showing transitions between elongated and round tumor cells. Most tumor cells have vacuolated or finely granular pink cytoplasm. x 500
FIGURE
552
BUREK, ZURCHER, AND HOLLANDER
3.-Round-cell sarcoma with area of slightly elongated cells having oval nuclei and variable amounts of pink cytoplasm. x 500 FIGURE 4.-Round-cell sarcoma with nearly all tumor cells showing vacuolated cytoplasm. Note bizarre giant cell. x 500 FIGURE
BUREK, ZURCHER, AND HOLLANDER
553
5.-Round cell sarcoma of vagina, with cystic spaces and infiltration into colon wall. x 18 FIGURE 6.-Diffuse stromal (submucosal) sarcoma of cervix. Tumor cells extend from ulcerated mucosal surface (M) into outer smooth muscle wall (SM). x 80 FIGURE
554
BUREK, ZURCHER, AND HOLLANDER.
