10TH ANNIVERSARY ARTICLES Hereditary Nonpolyposis Colorectal Cancer (Lynch Syndromes I & II) Genetics, Pathology, Natural History, and Cancer Control, Part I Henry T. Lynch, Stephen Lanspa, Thomas Smyrk, Bruce Boman, Patrice Watson, and Jane Lynch

ABSTRACT: Hereditary nonpolyposis colorectal cancer (HNPCC) is common, accounting for about 4-6% of the total colorectal cancer burden. It is heterogeneous and appears to be delineated into two clinical subsets, Lynch syndromes I and II. Lynch syndrome I is characterized by an autosomal dominantly inherited proclivity to early onset colonic cancer with proximal predominance and an excess of multiple primary colonic cancer. Lynch syndrome II has all of these features plus extracolonic cancer sites, the most common of which is endometrial carcinoma. The lack of premonitory physical signs or biomarkers of HNPCC makes diagnosis difficult. A careful family history, tempered by an understanding of the clinical and pathologic features of HNPCC, is the key to its assessment. This paper reviews HNPCC's natural history, its integral extracolonic cancer associations, its differential diagnosis, surveillance, and management strategies. Attention is focused upon the need for biomarker research in the interest of improving control of HNPCC. INTRODUCTION A m o n g n o n c u t a n e o u s malignancies, colorectal cancer (CRC) is second in incidence after carcinoma of the lung in the United States and many other western countries. A n estimated 157,500 new cases will occur in the United States in 1991 (112,000 will involve the colon and 45,500 the rectum), where the estimated mortality will be 60,500 (53,000 colon, 7,500 rectum) [1]. There has been little change in survival from CRC during the past 3 decades, despite advances in chemotherapy, radiation therapy, and surgery. The lack of therepeutic progress has contributed to increasing interest in CRC's etiology. Genetics plays a particularly important role in this regard, as its ability to predict risk is often profound. In the best k n o w n example, familial adenomatous polyposis (FAP), CRC can be expected to occur by age 50 in 100% of patients with colonic polyposis [2, 3]. Recognition of HNPCC is more difficult because it lacks the distinctive premonitory markers. The CRC risk in HNPCC will be approximately 50% to a first-degree relative of a syndrome cancer-affected patient in the direct genetic From the Department of PreventiveMedicine (H. T. L., P. W., J. L.), Department of Internal Medicine (H. T. L, S. L., B. B.), and Departmentof Pathology(T. S.), CreightonUniversitySchool of Medicine,Omaha, Nebraska.

Address reprint requests to: Henry T. Lynch, M.D., Dept. of Preventive Medicine, Creighton University School of Medicine, California at 24th Street, Omaha, NE 68178. Received August 6, 1990; accepted September 24, 1990.

143 © 1991 ElsevierScience PublishingCo., Inc. 6 5 5 Avenue of the Americas,New York, NY 10010

Cancer GenetCytogenet53:143-160 (1991) 0165-4608/91/$03.50

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Historical Background Historically, the concept of a genetic proclivity to CRC in the absence of florid polyposis of the colon dates to Warthin's original observations on family G, initiated in 1895 and published in 1913 [4]. In the mid-1960s, Lynch and Krush [5] updated family G when they were provided all of Warthin's original pedigrees, medical, and pathology records. This offering followed the description of an autosomal dominantly inherited syndrome of colon cancer in the absence of multiple colonic polyps in two extended kindreds [6]. Since that time, investigators have continued to provide further detailed definition of the syndrome's natural history, including an expansion of cancer susceptibility sites.

Differential Diagnosis of HNPCC Family history remains the only measure for the recognition of HNPCC. Soberingly, in spite of the wealth of knowledge that can be accrued through a carefully obtained family history, the cancer family history is notorously neglected in the evaluation of most patients. The clinician, however, must make a distinction between HNPCC and other hereditary CRC counterparts, particularly the several FAP syndromes. The exclusion of FAP syndromes can often be readily performed through recognition of multiple (particularly florid) colonic polyps or, in the case of the so-called Gardner's variant, the presence of extracolonic signs such as osteomas, cutaneous cysts, desmoid tumors, and congenital hypertrophy of the retinal pigment epithelium (CHRPE) [7]. One must also consider problems of heterogeneity in the FAP syndromes, including variable expressivity of the colonic adenomatous polyp expression [8]. Consideration must also be given to the proposed hereditary isolated common polyp-colon cancer syndrome, as described by Butt et al. [9] and Cannon-Albright [10]. This disorder may be difficult to distinguish from HNPCC and, to a lesser extent, the FAP syndromes. Significant extension of the pedigree will be important in deriving these distinctions. HNPCC must also be distinguished from familial CRC (two or more first- or seconddegree relatives with CRC). When considering familial aggregation as well as sporadic occurrences of CRC, one must realize how common CRC is in the general population, particularly in Western industrialized nations. Hence, multiple case families will be encountered frequently on the basis of chance alone. The differentiation of all forms of familial or hereditary clusters of CRC from HNPCC will require attention to natural history, age at onset, multiple primary cancer, and site predilection within the colon

[3]. Diagnostic Distinction Between Lynch Syndromes I and II HNPCC includes two variant forms: Lynch syndrome I, with an autosomal dominantly inherited susceptibility [11] to early onset colorectal cancer in the absence of diffuse polyposis (average age 44 years), a predominance of cancer proximal to the splenic flexure (approximately 70%), and an excess of synchronous and metachronous colonic cancers (> 40% at 10 years after initial CRC); and Lynch syndrome II, which shows all of the above features plus an integral association of endometrial carcinoma,

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145

Table 1 Cardinal features of HNPCC 1. 2. 3. 4.

Early age of onset. Proximal colon cancer involvement. Increased incidence of synchronous and metachronous colon cancers. Increased occurrence of multiple primary cancers with specific pattern: predominance of CRC with carcinoma of endometrium, ovary, stomach, ureter, and renal pelvis (full tumor spectrum remains elusive). 5. Autosomal dominant inheritance pattern. 6, Site-specific colonic cancer HNPCC subset (Lynch syndrome I). 7. An HNPCC subset characterized by specific pattern of extracolonic adenocarcinomas (Lynch syndrome II).

as had been defined in the early studies by Lynch et al. [6] [Table 1). The extracolonic cancer spectrum has increased in this disorder. Recent studies expanding the spectrum of extracolonic tumor sites provide another clue for the clinician considering a diagnosis of HNPCC. These have included cancers of the stomach [12], larynx [13], urological system (particularly transitional cell carcinoma of the ureter and renal pelvis) [14], ovary [15], pancreas [16], small bowel [17, 18], and bile duct [19].

Cancer Probability Estimates and Extracolonic Cancer Sites in the Lynch Syndromes While the family history remains the key to HNPCC's diagnosis, in many circumstances obtaining information on the extended family may not be possible. However, identification of certain components of HNPCC in the nuclear family may provide important clues for a presumptive diagnosis. This may be sufficient for exercising sound surgical judgment, particularly with respect to performing a subtotal colectomy as opposed to a more limited colonic resection in a given patient presenting with initial CRC. It may be equally valuable for initiation of a highly targeted surveillance program for that patient's primary relatives. Probability estimates for syndrome cancer may be useful for risk consideration. Consider the scenario of a nuclear family of eight, comprised of both parents with a sibship of six. Two family members develop proximal colon cancer before age 40. SEER data indicate that the probability of manifesting colon cancer by age 40 is 7 x 10 -4 . About 35% of colon cancer occurs proximal to the splenic flexure. If all cancer diagnoses in this family were considered as independent, then the probability of two cases of proximal colon cancer at less than age 40 would be equal to 1.7 x 10 -6 or 2 in a million. The probability of 3 cases of proximal colon cancer at less than age 40 would equal 8.7 x 10 -1°, or 1 in a billion. In order to appreciate the probability for the onset of colon and endometrial carcinoma prior to age 40, we compiled their likelihoods based on age-specific colon and endometrial cancer incidence from the SEER data. If the probability of manifesting colon cancer by age 40 is 7 x 10-4, and of endometrial carcinoma by age 40 is 4.4 x 10-4, then the probability of a female having both colon and endometrial cancer onset prior to age 40, if these diseases are unrelated, is (0.00044)(0.0007), or 3 in 10 million. While these age-specific cancer computations do not portend etiologic significance, they do, nevertheless, provide a basis for comprehending their relative frequencies. By assessing the clinical significance for early onset colorectal and endometrial cancer, including their combination in a single patient, we are provided an appreciation for their chance expectations in the general population. Review of a Lynch syndrome II pedigree (Fig. 1) will show examples of these features occurring repetitively in patients in a highly predictable manner given their autosomal dominant mode of genetic transmission.

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Certain minimal probabilistic features of colon and endometrial cancer occurrences may be helpful in considering an HNPCC diagnosis. Early onset CRC or endometrial cancer occurrence are extremely important observations. Recently, Vasen et al [20] studied the tumor complement in 24 HNPCC kindreds from Holland. CRC was present in 104 patients, where the mean age at diagnosis was 46 years. In four of the families, CRC was the only type of cancer to occur, a finding consonant with the Lynch syndrome I variant. Sixty-five extracolonic tumors were observed in 20 of the kindreds. Carcinoma of the endometrium was present in 16 patients from 12 families; carcinoma of the stomach was present in 10 patients from five families, primarily in the older generations; and urinary tract tumors were found in eight patients from four families. Other forms of cancer were observed, but at a lesser frequency. These investigators concluded that carcinoma of the endometrium, stomach, and urinary tract were integral to the hereditary tumor spectrum of HNPCC. The frequency of specific types of cancer has recently been analyzed in members of 23 HNPCC families from the Creighton University/Hereditary Cancer Institute resource. The members of these families were classified into risk categories, as follows: all persons not descendant from the progenitors were classified "married in." Of those remaining, all with colorectal cancer or endometrial cancer were classified as "affected"; those with affected offspring were classified as "unaffected gene carriers"; these cases and all their first-degree relatives were classified as "high risk." All remaining family members, and the "married-in" family members, were classified as "low risk." We compared the observed numbers of cancer diagnoses in each risk group to the expected numbers, based on general population incidence data. Only invasive cancers with a specified primary site documented by pathology report, medical records, or death certificate were included. Statistical tests of the hypothesis that the observed number of cancers differed from the expected number were performed, and standardized incidence ratios (actual/expected numbers of cancers) were calculated, as an approximation of the relative risk. The high-risk group included 1320 individuals. Of these, 302 were affected by colorectal and/or endometrial cancer, and 39 were classified as unaffected gene carriers because of their pedigree position. The remainder were first-degree relatives of these cases. Members of this high-risk group had significantly (p < 0.05) more cancer diagnoses at specific sites than expected. Sites where cancer was found to occur in excess included stomach, small intestine, biliary system, kidney/ureter, and ovary. No differences were found between males and females in the cohort, except for the excess of ovarian cancer. Details are provided in Table 2. Certain negative findings in the high-risk group are noteworthy. No excess of pancreatic cancer, lymphatic/hematopoietic cancer, laryngeal cancer, breast cancer, malignant brain tumors, or lung/bronchus cancer was detected. In fact, significantly fewer lung/bronchus cancer cases occurred than were expected (p < 0.05). None of the five reported cases occurred in the affected or unaffected gene carriers. The low-risk group included 6089 individuals. No significantly excessive numbers of cancer diagnoses were observed in the low risk group, either in any general organ system or in any specific site. The paucity of lung cancer in HNPCC is surprising; its explanation remains elusive. No difference in cigarette smoking history has been observed between our HNPCC families studied to date and that expected from the general population. We have vigorously pursued the occurrence of all anatomic sites, including lung cancer, and are confident that the methods employed have not encouraged under-reporting of lung cancer. While these findings might be attributable to chance, familial environmental factors, or a high frequency of deaths from earlier onset cancer of the colon, it is possible that some type of genetic mechanism may exist that, on the one hand,

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n . T . Lynch et al.

Table 2

Gastric, small intestine, biliary system, urologic system, and ovarian cancer in high risk HNPCC family members

Cancer site at diagnosis

Observed

Expected

Observed/expected ratio

Stomach 17 4.1 4.1 (p < 0.001) Histology: all adenocarcinoma/carcinoma Small intestine 10 0.4 25 (p < 0.001) Histology: 9 adenocarcinoma/carcinoma, 1 carcinoid Hepatobiliary system 7 1.4 4.9 (p < 0.05) Histology: 4 adenocarcinoma, 3 uncertain site, histology Urinary bladder 5 4.6 0.76 (ns} Histology: all transitional cell carcinoma Kidney 10 3.1 3.2 (p < 0.01) Histology: 3 renal cell, 7 transitional cell carcinoma Ureter 5 0.2 22 (p < 0.001) Histology: all transitional cell carcinoma Ovary 13 3.6 3.5 (p < 0.001) Histology: all adenocarcinoma/carcinoma Pancreas 6 4.1 1.4 (p > 0.05) Histology: all adenocarcinoma/carcinoma Lung/bronchus 5 12 0.4 (p < 0.05) No reports in putative gene carriers Breast 19 22 0.9 (p > 0.05) Histology: all adenocarcinoma/carcinoma

Median age 54 53 66 65 66 56 40 52 62 51

predisposes to colon cancer (Lynch syndrome I) as well as selected forms of extracoIonic cancer (Lynch syndrome II), but concomitantly "protects" against malignant transformation at certain specified anatomic sites, i n c l u d i n g the lung. No description of extracolonic lesions in HNPCC would be complete without m e n t i o n of the Muir-Torre syndrome. Clinical and pathology studies of cutaneous lesions may lead to the recognition of Muir-Torre features in certain HNPCC kindreds [21]. These comprise sebaceous hyperplasia, sebaceous adenoma, and sebaceous carcinoma, basal cell carcinoma with sebaceous differentiation, and/or keratoacan° thoma in association with visceral cancer, often multiple, and improved survival. These studies to date have been too limited to assess fully the potential of Muir-Torre features in the differential diagnosis of HNPCC [21, 22].

Histopathology of Hereditary Nonpolyposis Colorectal Cancer The diagnosis of HNPCC may be further supported by recognition of characteristic histologic features in the colon carcinomas of affected patients. Although several reports have suggested an excess of m u c i n o u s carcinoma in HNPCC, Mecklin et al. [23] were the first to offer a detailed histologic study of the colorectal cancers arising in the syndrome. They examined 100 carcinomas from 75 patients belonging to cancer families (defined by them as colorectal cancer in at least three first-degree relatives) and compared them with 75 sporadic cancers. The hereditary tumors were more likely to be poorly differentiated (24% vs. 12%, p < 0.05) and more likely to be m u c i n o u s (39% vs. 20%, p < 0.01) w h e n defined as a m u c i n o u s c o m p o n e n t accounting for more than 30% of a tumor. Three signet-ring carcinomas were seen in the hereditary group; there were no signet cell tumors in controls. Mecklin et al. [23] commented on the discrepancy between aggressive histologic features--poor differentiation, m u c i n o u s histology, signet cell m o r p h o l o g y - - a n d the reports of less aggressive clinical behavior in some HNPCC series [24].

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Our own experience with the histology of HNPCC is based on review of 95 CRC cancers from 77 patients representing 19 families. Pedigree analysis documented HNPCC, as defined above, in all 19 families. The number of cancers reviewed by us from each kindred ranged from two to 18, median four. The study was a retrospective review based on examination of material provided by outside laboratories. We analyzed parameters related to tumor stage (local extent of tumor, lymph node status), and grade (tubule configuration, growth pattern, host inflammatory response). A series of 40 consecutive colorectal cancers resected at Creighton's affiliated hospital in 1986-87 served as controls. Pathologists were not blinded to the source of slides under review. Our findings support Mecklin's assertion that poorly differentiated tumors are more common in HNPCC. Thirty-seven cancers (39%) from the hereditary group featured solid sheets of tumor cells with no visible gland lumens; only 13% of controls had this pattern (p < 0.01) (Fig. 2a). Mucinous carcinoma, diagnosed by us when the mucinous component comprised more than 50% of a tumor, accounted for 20% of HNPCC cases and 8% of controls ( p < 0.09). Like Mecklin, we found several examples of signet-cell carcinoma (4 of 95, 4%) in the HNPCC group (Fig. 2b). This rare variant makes up < 1% of all colorectal cancers and is considered to be an aggressive tumor [25, 26]. There were additional differences between HNPCC and controls: 35% of tumors from HNPCC families had a distinct cap of inflammatory cells at the advancing tumor edge and 40% had lymphocytic nodules in peritumoral tissue, the so-called Crohn'slike reaction [27]. The percentage of control cases positive for these parameters was 15% and 20%, respectively (p < 0.02 in both cases). The two groups also differed in terms of tumor stage at diagnosis. In 73% of HNPCC patients, there was tumor spread through the muscularis propria, compared to 87% of controls ( p < 0.08). While 48% of controls had metastases in regional lymph nodes, lymph node spread was documented in only 23% of HNPCC (p < 0.01). These differences are unlikely to be the result of enhanced surveillance in HNPCC because only one family was entered in a prospective screening program, and no tumor was diagnosed in an asymptomatic patient. Thus, the findings present a paradox: the carcinomas of HNPCC have aggressive histologic features in the form of poor differentiation and mucinous/signet cell histology, but they tend to be less advanced at diagnosis. In addition, two types of host response thought to confer favorable prognosis--peritumoral inflammation and Crohn's-like reaction [27, 28]--are more common in HNPCC than controls. As suggested by Mecklin, the patients from these HNPCC families do have a betterthan-expected prognosis, despite their propensity for poorly differentiated tumors. The actuarial 5-year survival for the 77 patients in this study was 82%. Histologic grade, an independent predictor in several studies [28, 29], had no significant effect on survival in these patients, nor did stage at diagnosis. Even patients with positive lymph nodes had a 5-year survival of 71%, compared to the 29-49% reported 5-year survival for node-positive patients in two recent studies [30, 31]. The long survival of HNPCC patients is particularly impressive in light of the occurence of multiple metachronous colon cancers in 20% of patients. While the pathologic paradox of HNPCC is not yet resolved, the findings provide additional clues to syndrome diagnosis: poorly differentiated, mucinous, or signetcell carcinomas should prompt a search for other indicators of HNPCC.

Surveillance and Management for Colon Cancer in the Lynch Syndromes Screening for colorectal cancer in HNPCC is predicated upon its natural history features (Table 3). The age of cancer onset is 15-20 years earlier than its occurrence in the general population. The youngest reported patient was a 14-year-old girl with colon cancer [32]. The mean age for colon cancer in our patients is 45.6 years [33].

150

Figure 2a Colonic carcinoma lacking gland lumen formation (poorly differentiated/. The well-demarcated border between tumor and stroma indicates an expanding growth pattern. There is host inflammatory response in the form of lymphocytes at the advancing edge of tumor; ×330. Figure 2b

Detail from another colon cancer showing signet-cell morphology; × 660.

HNPCC, Part I

Table 3

15 1

Classification, surveillance, and management strategies

Recommendations

FCC

Hereditary discrete common polyps and CC

Age for initiation of patient education

Age 30-35

Fecal blood test

Age 30-35, Age 30-35, and then and then semiannually semiannually Flex sis age 35 Flex sis age 35, and and every 2 annually yrs

Endoscopy° Colonoscopy

Surgery

Same as for general population indications

Extracolonic organs requiring special cancer surveillance

None

Age 30-35

HNPCC

FAP Preteens

Teens

Would not perform, Would not perform given endoscopic endoscopic surveillance surveillance Full Flex sis age 10 & Age 25, and every 1 yr; annually indirect ophthalmoscopy for CHRPE Subtotal colectomy Same as for general Prophylactic population subtotal indications colectomy vs. total colectomy w/pouch and reconstruction Endometrium, None Periampullary, stomach, ovary, urologic, (particularly in small bowel, bile Japanese), small duct, gastric, bowel, pancreas, breast sarcoma, thyroid, brain tumors; desmoids

° If polyps or other abnormalities,repeat 6 months to 1 year. CC = colon cancer. FCC = familial colon cancer. FAP = familialadenomatouspolyposis. HNPCC = hereditary nonpolyposiscolorectal cancer. CHRPE = congenitalhypertrophy of the retinal pigmentepithelium. We have arbitrarily suggested the initiation of screening at 25 years of age, or 5 years earlier than the earliest onset of colon cancer in a particular kindred. This includes full colonoscopy because of the proximal excess of colonic cancer in HNPCC. Concurrent with this, we perform endometrial aspiration/cytology studies on those w o m e n who are deemed to be at 50% risk for Lynch syndrome II. We also perform pelvic probe ovarian ultrasound on these patients, and we are studying CA-125 expression in their serum. At the time of diagnosis of colon cancer, because of the increased risk of metachronous lesions, a subtotal colectomy is performed. The proximal distribution of colon cancers in the Lynch syndromes and the higher incidence of morbidity with ileoanal anastomosis have led us to spare the rectum. The patients then undergo postoperative surveillance with flexible sigmoidoscopy.

Results of Surveillance Studies Love and Morrisey [34] performed colonoscopy on 42 consecutive asymptomatic members of Lynch syndrome kindreds. Eight patients had been diagnosed previously with cancer. Seventeen percent of these 42 patients had adenomatous polyps. Two of the polyps contained invasive carcinoma. Most of the lesions were b e y o n d the

152

H.T. Lynch et al. reach of the 25-cm sigmoidoscope. This was not truly a surveillance program for patients at 50% risk, as several patients previously had colon cancer. Mecklin and Jarvinen [35] reported a retrospective study of 122 patients with Lynch syndrome that showed a mean age of colon cancer at 41 years with proximal predominance. In a followup of 75 patients at 100% risk (previous diagnosis of co]orectal cancer) additional adenomas were found in 19% of these patients. Continued screening of 34 patients with previously identified cancer showed a high incidence of metachronous tumors (35%) within 3 years. In a study by Vasen et al. [36], 28 symptomatic patients underwent screening. Adenomas were found in 14 and carcinoma in six patients. Lanspa et al. [37] performed colonoscopy on 53 patients who were at 50% risk for the Lynch syndrome. Eight of these patients had polyps. No malignancy has been observed in these patients over a course of four years. Fleischer et al. [38] have recommended annual fecal occult blood tests and colonoscopy every 2-3 years beginning at age 20 in patients diagnosed with Lynch syndrome. We no longer recommend fecal occult blood tests in patients having periodic colonoscopy. Love and Morrissey [34] have suggested a 3-year interval for colonoscopy. Mecklin [39] recommends that screening begin at age 20 and continue to age 50. Vasen [36] also recommends that screening begin at age 20 but recommends lifelong screening because 18% of his cancer patients were older than age 60 at diagnosis. If the colon preparation is good, if the scope is passed to the cecum, and if adequate visualization is seen at the initial screen, a period of 2-3 years may be acceptable. For the present, we feel justified in yearly colonoscopy, though the efficacy of this approach must await longer followup to assess expense, patient discomfort, small risk of complications, and polyp/cancer yield. In the absence of a biomarker, colonoscopic surveillance appears to be the best method for prevention of colon cancer in these patients. In geographic areas where colonoscopy is not available, air-contrast barium enema with flexible sigmoidoscopy may be an acceptable alternative. In summary, in Lynch syndrome I, the primary surveillance and management focus is on the colorectum. In Lynch syndrome II, these strategies are more complex because of the excess risk for extracolonic cancer. Differentiation of these syndromes is also essential for investigation of genetic/environmental interaction in their etiology as well as for the development of strategies for biomarker investigations. Given the remarkable advances in molecular genetics during the past decade, attention must be focused appropriately upon the search for identification of the responsible gene(s) in HNPCC through the help of recombinant DNA techniques [40]. This research will undoubtedly facilitate improvement in HNPCC's surveillance and management strategies.

Flat Adenoma Syndrome Our surveillance studies of presumed HNPCC kindreds led to the recognition of one family with multiple (2-100) adenomas, frequently limited to the right colon. The adenomas had the gross and microscopic features described by Muto et al. [41] as flat adenomas. Grossly, the flat adenoma presents a raised appearance often with a central depression. Microscopically, the lesions are tubular adenomas in which the adenomatous change is concentrated near the luminal surface of the mucosa (Fig. 3a,b). We described this large colon cancer-prone kindred [42]; since that initial report, we have noted two additional families with vertical transmission of a phenotype consisting of flat adenomas with right-sided predominance and a relatively late age of onset of colorectal cancer [43]. These features may reflect a process that is clinically intermediate between HNPCC and FAP (Table 4). Polyp expression differs from FAP in terms of the number and anatomic distribution of adenomas; that is, affected patients develop dozens of adenomas, but seldom acquire 100, and never the thousands that

153

F i g u r e 3 a Small adenoma discovered in a colon resected for adenocarcinoma. The lesion is not raised above surrounding mucosa; × 66.

F i g u r e 3 b Detail from a, showing adenomatous tubules clustered in the luminal half of the mucosa, × 330.

154

H, T. Lynch et al. Table 4

Comparison of clinical features of flat adenoma syndrome, HNPCC, and FAP Flat adenoma syndrome

Onset Polyp number Gross path Polyp distribution Cancer distribution Other cancer

HNPCC

FAP

Late 0-100 Flat adenoma Mainly right sided

Early < 10 Typical or absent Mainly right sided

Early > 100 Typical Left or total

Mainly right sided

Mainly right sided

Random

Periampullary hepatoblastoma of unknown significance

Endometrium, other

Other Gl, ampultary

are characteristic of patients with FAP. The pancolonic mucosal involvement of FAP does not occur. Instead, it is often reduced to a segmental, proximal distribution. Biomolecular Markers Numerous cytologic and histopathologic markers have been investigated for their usefulness in HNPCC [44]. For example, tritiated-thymidine labeling of biopsies of normal appearing colonic mucosa from high-risk members of HNPCC families showed increased cell proliferation as compared to low-risk controls [45]. We have also reported on the occurrence of flat adenomas in colon cancer-prone kindreds as discussed above [42]. However, none of these markers has been proven to have acceptable sensitivity and specificity in determining individual risk for members in HNPCC families. A host of other marker studies on HNPCC are ongoing by our group and others, but are beyond the scope of this discussion. Initial evidence for the chromosome localization of an HNPCC gene is based on the positive linkage of this trait to the Kidd blood group (JK) (lod score + 1.88) [45]. When Lynch syndrome II families were analyzed separately from Lynch syndrome I, the lod score was highly significant (+ 3.19). The JK gene, assigned previously to chromosome 2, has been reassigned to chromosome 18 [46]. These studies tentatively support assignment of a Lynch Syndrome II gene to chromosome 18 [47]. However, this has not been confirmed in linkage studies using molecular genetic markers on this chromosome [43]. Insight relevant to the potential value of molecular markers for cancer susceptibility in HNPCC can be gleaned by extrapolating from the results on genetic studies involving familial adenomatous polyposis (FAP). FAP is a good prototype because of the presence of premonitory clinical features. Recently, two groups identified restriction fragment length polymorphic (RFLP) markers on the long arm of chromosome 5 that were tightly linked to the gene for FAP [48, 49]. Screening programs for the preclinical diagnosis of FAP are now incorporating genetic linkage data using a battery of RFLP probes on chromosome 5q [50, 51]. For example, Peterson et al. [52] reported on a study using chromosome 5 molecular genetic markers linked to FAP for screening atrisk relatives in FAP families. It was reported that the a priori 50% risk for relatives could be reduced to less than 0.5% by age 30 if they had an initial negative result on sigmoidoscopy and did not have the linked gene marker. Thus, molecular genetic markers linked to FAP at chromosome 5 can be used to augment the accuracy of premorbid diagnosis of at-risk individuals.

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Molecular markers will also be useful in understanding the basis for heterogeneity in hereditary colorectal cancer syndromes. For example, Nakamura et al. [53] studied six pedigrees, three having the FAP phenotype and three having Gardner's syndrome, by linkage analysis, using chromosome 5 markers, and found no evidence of genetic heterogeneity between the two phenotypes. Although the possibility that two different defective genes located close together on chromosome 5 cannot be eliminated, the simplest interpretation is that separate mutations within the same gene are generating the difference between the phenotypes. Leppert et al. [54] recently studied a family with variable number of adenomatous polyps (eight family members had two to 40 colonic polyps) and reported positive genetic linkage with DNA markers previously shown to be linked to the FAP locus. They conclude that mutations at the genetic locus for FAP may be the cause of other more subtle syndromes involving an inherited susceptibility to colonic adenomatous polyps and colorectal cancer. A recent gene linkage study on an extended flat adenoma kindred also showed positive linkage to markers linked to FAP at chromosome 5q21 (lod score 2.7) [43]. Interestingly, this flat adenoma kindred shows strikingly similar genetic and phenotypic features with the kindred reported by Leppert et al. that also had flat adenomas present (personal communication, Randall Burt, MD, 1990). Thus, molecular markers will probably prove to be very useful for the classification of hereditary colorectal cancer given the extant heterogeneity of the disease [55]. The development of colorectal cancer in hereditary cases appears to result from the acquisition of several additional specific genetic changes [56]. For example, Law et al. [57] reported allelic loss in Lynch syndrome patients on chromosomes 5 and 18, and Boman et al. [58] reported allelic loss in FAP patients on chromosome 18. Sporadic colorectal cancers also show chromosome 17p allelic deletions and the p53 gene on chromosome 17p is mutated in these tumors [59, 60, 61], suggesting that p53 inactivation accounts for the observed chromosome 17 deletion. Recent studies have also shown chromosome 18 deletions in sporadic colorectal cancers [58, 61], which may represent the loss of a tumor suppressor gene and a candidate gene (DCC) has recently been isolated by Fearon et al. [62]. As in the case of sporadic colorectal carcinomas [63], it is tempting to speculate that the accumulation of these specific genetic changes in hereditary colorectal cancer may have prognostic significance. Molecular studies on colorectal cancers from the general population suggest that germinal mutations occurring in hereditary cancer syndromes may involve the same or similar genes that are affected somatically in the development of sporadic colorectal carcinomas. For example, we and others have reported that chromosome 5q allelic deletion occurs in 25 to 60% of sporadic cases implying that the FAP gene is lost or inactivated in these colorectal tumors [64, 65, 66]. Thus, it will be important to investigate genes that have previously been shown to be deleted in sporadic colorectal cancers such as the p53 gene on chromosome 17 and the DCC gene on chromosome 18 by linkage analysis of HNPCC. The finding of the HNPCC gene location will have potentially greater significance than even the discovery of the FAP gene. This is because of the greater frequency of HNPCC as compared to FAP, the absence of premonitory physical signs in the Lynch syndromes, and the frequent occurrence of carcinomas at extracolonic sites in HNPCC.

DISCUSSION

During the past two decades, there has been an explosive increase in the awareness of hereditary factors in CRC. This knowledge should now become available to the clinician in the everyday practice setting. To this end, physicians must gain a better

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H.T. Lynch et al. understanding of genetics, natural history, and expression of hereditary cancer syndromes. HNPCC (Lynch syndromes I and II) have been found to be relatively common. When improved diagnostic methods, including biomarkers, become available, and when a more complete understanding of its heterogeneity emerges, including its tumor spectrum, we anticipate that its frequency will exceed its present estimate of approximately 4-6% of the total CRC burden [39]. Clearly, HNPCC poses a major public health problem [3]. The designation HNPCC is not entirely appropriate in that it implies an absence of colonic polyps. In fact, adenomatous colonic polyps do occur in HNPCC with approximately the same frequency as they occur in individuals in the general population [23, 25, 34]. Lanspa et al. [371 confirmed these findings among Lynch syndrome at-risk patients as part of a colonoscopy screening program. Initially, the prevalence of adenomas in this cohort was found to be greater than in an unselected reference group. However, one of the families which was included in our HNPCC cohort was subsequently found to be a flat adenoma kindred [42]. We now believe that the flat adenoma syndrome differs from HNPCC. When we excluded this flat adenoma-prone family from our statistical analysis, the frequency of colonic adenomas was found to be comparable to general population expectations. Of interest was an excess of proximal location for the colonic adenomas in the flat adenoma kindred and in the HNPCC cohorts, a finding which parallels the colonic cancer incidence in HNPCC (Table 4). Recognition of the Lynch syndromes is wholly dependent upon a well orchestrated family history. Unfortunately, in the usual clinical practice setting, where there is often a lack of attention to detail in the family history, the disorder frequently goes undiagnosed. All too often, HNPCC is not recognized until a family has suffered an inordinate amount of cancer morbidity and mortality. The relatives themselves often become alarmed and seek medical help through their own "discovery" that they represent a "cancer family." Even in this setting, unless the cardinal facets of HNPCC's natural history are known to the physician, surveillance and management strategies will be inadequate. In three decades of experience in the investigation of more than 100 extended HNPCC kindreds, we have repeatedly encountered patients in whom the hereditary nature of their cancer-prone problem was either completely ignored and/or mismanaged by physicians. Some genetically at-risk patients were considered to have a familial CRC predilection wherein the natural history of cancer expression was believed to be comparable to expectations from the general population. In many cases, affected patients were treated with less than a subtotal colectomy for initial colonic cancer. Predictably, they manifested metachronous CRC, sometimes at an advanced stage with a fatal consequence. Certain of the at-risk women were successfully treated for CRC, but their proclivity to gynecologic cancer (carcinoma of the endometrium and/or ovary) was ignored. In order for improved cancer control of HNPCC, many barriers to the full evaluation of the cancer family history need to be overcome. These include problems in the maintenance of privacy, confidentiality, and the like in the course of family studies, all of which pose their own ethical and even medical-legal implications [3]. There have been medical-legal concerns about the responsibility of physicians in the evaluation of high-risk patients and families. This concern has been receiving increasing attention in direct proportion to the acquisition of knowledge about the etiologic role of genetics in cancer. It is therefore appropriate to ask the question as to whether or not the standard of care relevant to the applicaton of genetics into the management strategies of cancer-prone families has yet emerged. This is important to the clinician because the term "standard of care" is recognized as a legal term, which harbors the potential for malpractice liability if the standard of care is ignored in a given case. This concept encompasses many issues which go beyond the purview

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of this report, central of which is the necessity of the physician to not only compile the family history but, moreover, to act upon its clinical implications. For example, failure to perform full colonoscopy as part of screening, or failure to perform a subtotal colectomy for the management of initial cancer in the Lynch syndromes, may achieve the same medical-legal concern as that given to the failure to diagnose and/or perform prophylactic colectomy in FAP. Given these facts, there is clearly a need for the mounting of intensive patient and physician educational programs about HNPCC. This may soon become a reality in light of the recently developed International Hereditary HNPCC Collaborative Group. The mission for this group is focused upon a better understanding of the natural history of HNPCC, improvement in understanding its diagnostic criteria, development of cost effective surveillance and management strategies, and most important, fostering a search for biomarkers of acceptable sensitivity and specificity to its deleterious genotype(s). In conclusion, we are convinced that cancer's morbidity and mortality in the Lynch syndromes can be successfully ameliorated through increased physician awareness of the syndrome's existence, coupled with meticulous attention to the family history in at-risk patients. Education about the genetics and natural history of the disorder(s) should begin in the early teens. Patients and their physicians must become allies in the cause of early detection and highly targeted management. It will then be imperative that all individuals who have been identified as members of HNPCC kindreds be kept under lifelong surveillance. Compliance will undoubtedly become a formidable problem in some circumstances. Part of the problem of compliance will relate to the expense of this surveillance. We are hopeful that this component of the compliance issue may be mollified through better participation of third-party carriers. We gratefully acknowledge support from Grant # 5 R01 CA 42705-03 and Council for Tobacco Research, USA Inc, Grant 1297 CR2.

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