1 Division of Molecular Genetic Epidemiology, German Cancer Research Center (DKFZ), Heidelberg, Germany; 2 Department of Biosciences at Novum, Karolinska Institute, Huddinge, Sweden
Received 29 September 2003; revised 2 December 2003; accepted 22 December 2003
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ABSTRACT |
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Endometrial cancer is the second most common lesion within hereditary non-polyposis colorectal cancer (HNPCC) syndrome. The importance of the non-HNPCC genetic predisposition to endometrial cancer is unclear, and the familial aggregation of endometrial cancer after exclusion of HNPCC families may offer valuable clues about the involvement of non-HNPCC-related genes.
Patients and methods:
The families of the nationwide Swedish Family-Cancer Database were classified as HNPCC families according to the Amsterdam I or II, the modified Amsterdam, the Japanese and the Bethesda criteria. Standardized incidence ratios (SIRs) for endometrial cancer when parents or siblings were diagnosed with cancer at the most common sites were calculated before and after exclusion of HNPCC families.
Results:
The proportion of individuals in the families with endometrial cancer was highest when the criteria required three cancers within a family or multiple HNPCC-related cancers in the same individual. Consideration of the Amsterdam or the Japanese criteria hardly reduced the familial aggregation of endometrial cancer. After exclusion of families that fulfilled the Bethesda criteria, SIRs were significant when the parents were diagnosed with endometrial or thyroid gland cancers; 75.7% (95% confidence interval 60% to 99.1%) of the familial cases of endometrial cancer were not related to HNPCC according to the Bethesda criteria. The reduction of SIRs for cancers at the colon, pancreas, prostate and ovary was limited when the Bethesda criteria were applied. However, the Bethesda criteria identified most of the familial aggregation when endometrial cancers were diagnosed before the age of 55 years.
Conclusions:
The data suggest that additional effects, not related to HNPCC, contribute to the familial aggregation of endometrial cancer.
Key words: Amsterdam criteria, Bethesda guidelines, endometrial cancer, familial risk, HNPCC, Japanese criteria
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Introduction |
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Different clinical criteria have been established to classify HNPCC families. The Amsterdam criteria I [8], the modified Amsterdam criteria [9, 10] and the Japanese criteria [11] only consider colorectal cancer (Table 1). Endometrial, small bowel, ureter and renal pelvis cancers are included in the Amsterdam II criteria [5]. The Bethesda guidelines, developed to guide the analysis of microsatellite instability, additionally consider stomach, ovarian and hepatobiliary tract cancers, as well as colon adenomas [7]. Even sebaceous gland adenomas, also features of MuirTorre syndrome, cancers of the nervous system and keratoacanthomas have been associated with the HNPCC syndrome [57, 12].
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Patients and methods |
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Only families from the database with at least four generations were included in the study. If one founder parent of the family was missing or married several times, the family was not considered. Families were classified as HNPCC families according to the Amsterdam criteria I or II, the modified Amsterdam criteria, the Japanese criteria and the Bethesda criteria, as described in Table 1.
Follow-up started at birth, immigration date or first year of the study (1961), whichever came latest. Follow-up terminated at diagnosis of cancer, death, emigration date, 31 December 2000 or the age of diagnosis as specified in the study. The standardized incidence ratio (SIR) was used to estimate familial relative risk. SIR was based on only parents diagnosed (SIRparent) or only siblings diagnosed (SIRsibling) as probands. The SIR was calculated as the ratio of observed to expected number of cases. The expected numbers were computed from age (5 year bands), parity (six groups from any parturition to more than five parturitions), socioeconomic status (six groups), age at first birth (five groups, 5 year bands between before age of 20 and after age of 35) and residential area (four groups) standardized incidence rates. The confidence intervals (CIs) were calculated assuming a Poisson distribution [14]; 99% CIs are presented to address the issue of multiple comparisons.
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Results |
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The number and size of families that fulfilled the different clinical criteria are presented in Table 2. Amsterdam I criteria required three cases of colorectal cancer within a family, and classified 18 families. Amsterdam II criteria required three cases of colorectal, endometrial, small bowel, ureter or renal pelvis cancer within a family, and classified 37 families. Among the 5593 persons in the second generation diagnosed with colorectal cancer, 35 (0.6%) belonged to families that fulfilled the Amsterdam I criteria and 48 (0.9%) belonged to families that fulfilled the Amsterdam II criteria. Set 1 of the modified Amsterdam criteria and set B of the Japanese criteria required two diagnosed individuals in a family. The modified Amsterdam criteria classified 382 families and the Japanese criteria classified 279 families. Condition 2 of the Bethesda criteria required multiple HNPCC-related cancers in one individual, and classified 2826 families. Condition 3 of the Bethesda criteria rested on two cases within a family, and classified 368 families. Condition 4 of the Bethesda criteria was based on one colorectal or endometrial cancer before the age of 45 years, and classified 4403 families. Condition 7 of the Bethesda criteria considered early-onset colorectal adenomas, and classified 259 families.
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Table 3 shows the number of cases of endometrial cancer, SIRparent and 95% CIs for women when their parents were diagnosed with cancer at any site. SIRparent in the general population was significant (95% CI did not include 1) for endometrial, thyroid gland, colon, prostate and all cancer sites, with a range from 2 to 1.09. The 99% CI of SIRparent did not include 1 for the endometrium, colon, prostate and all sites. The lowest confidence limit of the SIRparent was >0.9 for pancreas, urinary bladder and colon in situ. After exclusion of Amsterdam I or Amsterdam II families, the SIRs were almost identical to those for the general population, and are not presented. SIRs were only slightly modified when HNPCC families were excluded according to the modified Amsterdam criteria or the Japanese criteria. If Bethesda families were excluded, SIRparent decreased, and was only significant for the thyroid gland (1.95), the endometrium (1.92) and all sites (1.07); the 99% CI of SIRparent for the endometrium did not include 1 when the Bethesda criteria were applied. The Bethesda criteria identified 17 pairs where both a mother and a daughter had endometrial cancer. Among the 17 daughters, eight were diagnosed with endometrial cancer before the age of 45 years, but none was affected by multiple endometrial cancer.
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Discussion |
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Only families with at least four generations were included in the study, but the maximum age of individuals in the second generation (68 years) is a limitation of the present analysis. The frequency of patients with colorectal cancer in the second generation fulfilling the Amsterdam criteria I was 0.6% (95% CI 0.4% to 0.9%) and 0.9% (95% CI 0.6% to 1.1%) of the patients that fulfilled the Amsterdam II criteria. These figures are in agreement with the frequency of 1.2% (95% CI 0.1% to 2.2%) reported for HNPCC in a recent Swedish study [16]. However, this study relied entirely on registered data of complete coverage. The issue of ascertainment bias, when the clinical criteria require three cases within a family, has been discussed previously [17]. Another limitation of this study was that no signet-ring histology could be considered (condition 6 of the Bethesda criteria); however, this omission was unlikely to have any large effect on the results.
The International Collaborative Group on HNPCC established the Amsterdam I criteria to provide a basis for uniformity in collaboration studies [8]. The criteria were restrictive, since extracolonic malignancies, clearly an important component of HNPCC, were not considered, and small families were unlikely to fulfil the criteria [3]. Only 18 families from the database were classified as Amsterdam I families. On the other hand, when Amsterdam I criteria were met, the chance of HNPCC was high, i.e. Amsterdam I criteria aimed at specificity more than sensitivity. Although Amsterdam I criteria are widely accepted and used in clinical counselling [5], some investigators consider the criteria to be too strict [7, 18], and alternatives have been developed. The modified Amsterdam criteria [810] require two diagnosed relatives, and consider early-onset endometrial cancer. The Japanese criteria [11] also classify families with two cases, and additionally take into consideration the clinical features of HNPCC: early-onset, multiple synchronous or metachronous colorectal cancers, and right colon involvement. The Bethesda guidelines proposed by Rodriguez-Bigas et al. [7] target the evaluation of colorectal tumors for microsatellite instability or mismatch repair gene testing. The Bethesda guidelines are less restrictive and more sensitive, but also less specific, than the Amsterdam criteria. The most recent Amsterdam II criteria [5], developed by the International Collaborative Group on HNPCC, include colorectal, endometrial, small bowel, ureter and renal pelvis cancers, but keep the requirement to three cases in the family. In this study, 37 families were classified according to Amsterdam II and 7296 families were classified according to the Bethesda criteria as HNPCC families. The proportion of individuals in the Amsterdam II families with endometrial cancer was 4.06%, compared with 0.89% in the Bethesda families. Syngal et al. [19] compared different clinical criteria for HNPCC by using the sensitivity and specificity for mutations in MSH2 and MLH1 as a distinctive feature. A comparison of the clinical criteria based on the risks for specific sites, such as the endometrium, would be also of great interest.
We found significant risks for endometrial cancer when the relatives were diagnosed with colon, endometrial, thyroid gland, ovarian and prostate cancers. The lowest limit of the 95% CI was >0.9, even when parents were diagnosed with pancreatic, urinary bladder and colon in situ cancers (Table 3), and when sisters were diagnosed with breast cancer (Table 4). The link between pancreatic, urinary bladder and colon in situ cancers with HNPCC is well established, while the inclusion of the breast among the HNPCC cancer sites remains controversial. The likelihood of HNPCC contribution in the association of endometrial cancer with other cancers depended on the age of onset and the specific cancer site. SIRs for the colon were not significant after exclusion of the Bethesda families, but the lowest confidence limit remained high, and some association between colon and endometrial cancer, independent of HNPCC, is probable, although it is also plausible that the clinical criteria did not encompass all HNPCC cases. A similar interpretation held when parents were diagnosed with colon in situ, pancreas, prostate and urinary bladder cancers. SIRs when sisters were affected with breast or ovarian cancer remained relatively high, even in the Bethesda-negative cases. These data suggest that HNPCC plays a minor role, if any, in the association of breast/ovary and endometrial cancer. In general, the reduction of SIRs when the Bethesda families were excluded depended largely upon the age at diagnosis. If cancers were diagnosed at any age in parents (Table 3), SIRs remained significant for endometrial and thyroid gland cancers after exclusion of the Bethesda families. In all, 75.7% (95% CI 60% to 99.1%) of the familial cases of endometrial cancer were probably not related to HNPCC. If only conditions 13 of the Bethesda criteria were considered, as has recently been recommended [19], the proportion of endometrial cancers not related to mismatch repair gene mutations increased to as much as 87.1%. A higher proportion of the familial aggregation was recognized by the Bethesda criteria if cancers were diagnosed before the age of 68 years in siblings (Table 4). Results presented in Figure 1 show the performance of the Bethesda criteria for endometrial cancer diagnosed at different ages. The SIR for familial endometrial cancer, not related to HNPCC, increased with increasing ages of diagnosis. Infrequent mismatch repair gene alterations (i.e. MSH6 mutations) could explain in part the aggregation of late-onset endometrial cancer [20].
In conclusion, the data suggest that germline mismatch repair mutations explain a limited amount of the familial aggregation of endometrial cancer. The remaining genetic and environmental causes of the aggregation are a challenge for future studies.
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Acknowledgements |
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FOOTNOTES |
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