Affiliations of authors: Department of Internal Medicine, Division of Molecular Medicine and Genetics (BLN, JDB, LPT, SBG), Department of Epidemiology, School of Public Health (BLN, SBG), and Department of Human Genetics (SBG), University of Michigan Medical School, Ann Arbor, MI; Department of Community Medicine and Epidemiology, Carmel Medical Center and Technion Faculty of Medicine, Haifa, Israel (GR); Clalit Health Services National Cancer Control Center, Haifa (GR, RA).
Correspondence to: Stephen B. Gruber, MD, PhD, MPH, Division of Molecular Medicine and Genetics, 4301 MSRB III, Box 0638, 1150 W. Medical Center Dr., University of Michigan, Ann Arbor, MI 48109-0638 (e-mail: sgruber{at}umich.edu)
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Three founder mutations, BRCA1 187delAG (formerly known as 185delAG), BRCA1 5385insC (formerly known as 5382insC), and BRCA2 6174delT, have a combined prevalence exceeding 2% in Ashkenazi Jews, facilitating analyses of the phenotypic spectrum of tumors in gene carriers (7). In 1997, a large nonpopulation-based study of Ashkenazi Jews from the Washington, DC, metropolitan area (7) compared the cancer histories of relatives of mutation carriers with those of relatives of non-carriers. This study, which used a kincohort design, found that the incidence of colon cancer among relatives of BRCA1/2 founder mutation carriers was not elevated compared with that among relatives of non-carriers. Two recent case patient series investigated the prevalence of these founder mutations in unselected case patients with colorectal cancer, and these case series report contradictory results and conclusions concerning the association between BRCA1/2 founder mutations and colorectal cancer (8,9). Compared with the 2% mutation prevalence found in the Struewing study (7), one case series found no statistically significantly increased founder mutation prevalence in case patients with colorectal cancer (1.78%), whereas the other study found a statistically significant increase in the prevalence of founder mutations among case patients with colorectal cancer (3.5%) (8,9).
Several studies have investigated the possibility of familial aggregation of breast cancer and colorectal cancer, and at least three show a positive association (1012). Phipps and Perry (10) demonstrated an increased incidence of colorectal cancer in relatives of patients with familial breast cancer compared with that of relatives of patients with sporadic breast cancer. Nelson et al. (11) found that colon cancer incidence was increased among women with a family history of breast cancer, although this risk estimate did not achieve statistical significance. Slattery and Kerber (12) reported that men with a first-degree relative with breast cancer had an increased risk of colorectal cancer (odds ratio [OR] = 1.3, 95% CI = 1.02 to 1.66) and women with a first-degree relative with breast cancer also had an elevated risk of colorectal cancer (OR = 1.59, 95% CI = 1.25 to 2.03). Given the inconsistent results regarding the risk of colorectal cancer in BRCA1/2 mutation carriers, we conducted a planned interim analysis of the Molecular Epidemiology of Colorectal Cancer study. We investigated whether the three BRCA1/2 founder mutations and a family history of breast cancer are associated with the risk of developing colorectal cancer within a population-based casecontrol study of colorectal cancer.
![]() |
METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The Molecular Epidemiology of Colorectal Cancer study is an ongoing, population-based casecontrol study of case patients with pathologically confirmed, incident colorectal cancer diagnosed between March 31, 1998, and December 31, 2002, from the geographic region covered by the five major hospitals in northern Israel. Individually matched control subjects were identified from the Clalit Health Services database and matched for plus or minus 1 year of age, sex, the source clinic of the case patient, and ethnicity (Jewish versus non-Jewish). For each Molecular Epidemiology of Colorectal Cancer participant, blood, paraffin-embedded tumor specimens, and frozen tumor specimens (if available) were collected, and an in-person interview was performed. Between March 31, 1998, and December 31, 2002, 2409 case patients diagnosed with colorectal cancer were ascertained, and 2238 were approached and invited to participate. To date, 1438 case patients have consented to participate, and 1422 case patients completed in-person interviews and donated a blood sample. In addition, 1585 population-based control subjects without colorectal cancer consented to participate. These control subjects were identified from a list of individuals generated from the Clalit Health Services database who were matched by age, sex, clinic, and ethnicity (Jewish versus non-Jewish) to diagnosed case patients. This sampling strategy accounts for the slight overrepresentation of control subjects to case patients for this ongoing matched study. We elected not to exclude control subjects for whom we had data for this analysis, even when the case patient had not yet been recruited. A total of 1566 control subjects who completed an in-person interview and donated a blood sample were considered in this analysis. The 1585 control subjects who consented to participate included 53% of potentially eligible control subjects who participated when first approached, 22.4% of control subjects who were recruited from a pool of first-replacement control subjects, and 24.6% of control subjects who were recruited from second-replacement or higher-order control subjects. For matched analyses, the dataset was restricted to the 1217 matched pairs with complete genotyping and epidemiologic data. The study was approved by the Institutional Review Boards at the University of Michigan and Carmel Medical Center in Haifa. Written, informed consent was required for eligibility.
Family History of Cancer
Family histories of cancer were obtained by interviews of Molecular Epidemiology of Colorectal Cancer study participants. All children, siblings, parents, grandparents, aunts, and uncles were enumerated; for each relative, case patients and control subjects were asked to report whether that relative had ever been diagnosed with cancer. For each relative, up to three primary cancers, ages at diagnoses, and smoking history were recorded. Analyses reported are restricted to first-degree relatives (parents, siblings, and children). Pathology documentation of cancers among relatives was not systematically collected.
DNA Extraction and Genotyping
Genomic DNA was extracted from whole blood by use of a commercially available kit, according to the manufacturers protocol (Puregene DNA extraction kit; Gentra Systems, Research Triangle, NC). Genetic testing for BRCA1 187delAG was performed by restriction enzyme digestion, as previously described (13). BRCA2 6174delT was assayed by an allele-specific polymerase chain reaction as described (7). A modification of a published allele-specific oligonucleotide assay (14) was developed to genotype for BRCA1 5385insC. For the 5385insC polymerase chain reaction, each 20-µL reaction mixture contained 100 ng of genomic DNA, 10 mM TrisHCl (pH 8.3), 50 mM KCl, 1.5 mM MgCl2, all four deoxynucleoside 5'-triphosphates (each at 200 µM), AmpliTaq DNA Polymerase (Applied Biosystems, Foster City, CA) at 0.05 U/µL, 330 nM primer 20F, and 330 nM primer 20R, with primer sequences from Struewing et al. (7). Thermal cycling included an initial denaturation at 95 °C for 5 minutes, then 35 cycles of a 30-second denaturation at 94 °C, a 1-minute annealing at 60 °C, and a 1-minute extension at 72 °C, with a final 10-minute extension at 72 °C. Allele-specific oligonucleotide hybridization was performed as previously described (14), with the following two differences: the hybridization and wash steps were done at 56 °C, the wild-type probe was 5'-ACCTTTCTGTCCTGGGATTC-3', and the mutant probe was 5'-ACCTTTCTGTCCTGGGGATT-3' (14). Genomic DNA from patients with breast cancer known to have one of the three mutations 187delAG, 6174delT, or 5385insC served as positive control for each assay, and genomic DNA samples from patients with breast cancer who did not have the mutation of interest were used as negative controls for each assay. Each assay was validated against a panel of 38 known samples, with 100% sensitivity and specificity. In addition, all positive 187delAG, 6174delT, and 5385insC samples were confirmed by sequencing with an ABI 377 sequencer (Applied Biosystems) through the University of Michigan DNA Sequencing Core facility. Samples were genotyped for APC I1307K polymorphism, as previously described (14), because this polymorphism might be a low-penetrance susceptibility allele for breast cancer and thus should be considered a potential confounder of the putative associations between BRCA1/2 mutations or a family history of breast cancer and the risk of colorectal cancer.
Statistical Methods
To compare demographic characteristics between case patients and control subjects, two-sided Students t tests and 2 tests were performed with SAS version 8.02 (SAS Institute, Cary, NC). Genotypes and interview data from all case patients and control subjects and from only those of Ashkenazi Jewish descent (1002 case patients and 1038 control subjects) were used to calculate odds ratios from logistic regression. Unmatched and matched analyses used unconditional and conditional logistic regression, respectively. No substantive differences were observed between the matched and unmatched analyses, although the confidence intervals were wider for the matched data as a consequence of the smaller sample size of matched pairs.
In a kincohort analysis, we compared cancer risks among the relatives of BRCA1/2 mutation carriers and the relatives of BRCA1/2 mutation non-carriers. Each family member was considered to be at risk until the time of cancer diagnosis, death, or interview of the case patient or control subject. Cumulative cancer risk estimates were calculated with a KaplanMeier analysis and compared with the log-rank test (7,15,16). All statistical tests were two-sided.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
|
|
|
|
Within the Ashkenazi Jews, the cumulative risk of all cancers (except for breast and ovarian cancer) was statistically significantly greater in relatives of BRCA1/2 mutation carriers than in relatives of BRCA1/2 mutation non-carriers (Fig. 1, A, log-rank P = .047). Because gynecologic cancers are commonly misclassified, we also analyzed cumulative risk in relatives after excluding breast, ovarian, and endometrial cancer. Relatives of BRCA1/2 mutation carriers no longer had a greater cumulative risk of cancer than relatives of non-carriers (log-rank P = .23). Not surprisingly, the cumulative risk of breast and ovarian cancers was statistically significantly greater in relatives of BRCA1/2 mutation carriers than in relatives of non-carriers (Fig. 1, B, log-rank P<.001). Limited power existed to estimate cumulative risks of other cancer types, including colorectal cancer.
|
In unmatched, adjusted analyses stratified by BRCA founder mutation carrier status, no statistically significant difference in the risk of colorectal cancer associated with a family history of breast cancer in a first-degree female relative was observed within the Ashkenazi Jews. However, our study had limited power to address the potentially important interaction between BRCA1/2 founder mutation carrier status and breast cancer family history on the risk of developing colorectal cancer (for BRCA1/2 founder mutation carriers with a first-degree female relative with breast cancer, OR = 0.61, 95% CI = 0.11 to 3.37; for BRCA1/2 founder mutation non-carriers with a first-degree female relative with breast cancer, OR = 1.13, 95% CI = 0.77 to 1.65; P for interaction = .49).
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
BRCA1 and BRCA2 founder mutations do not confer a risk for colorectal cancer as high as the fourfold increased risk previously reported (1). Although we cannot exclude increases in the risk of colorectal cancer related to BRCA1/2 founder mutations, we suggest that any risk is unlikely to be clinically significant. This conclusion extends the recent findings of Thompson and Easton (4), who reported that BRCA1 mutation carriers were not at a statistically significantly increased risk of colorectal cancer compared with non-carriers. Although that study (4) noted a statistically significant discrepancy between the risk of colon cancer and the risk of rectal cancer in BRCA1 mutation carriers, we detected no statistically significant difference between the risk of colon cancer and the risk of rectal cancer in BRCA1 and BRCA2 mutation carriers. Within the study by Thompson and Easton (4), stratification by sex revealed that female BRCA1 mutation carriers had a twofold increased risk of colorectal cancer (RR = 1.94, 95% CI = 1.21 to 3.10), whereas male BRCA1 mutation carriers had no increased risk of colorectal cancer (RR = 0.93, 95% CI = 0.6 to 1.44). Our study did not identify any statistically significant differences in the risk of colorectal cancer associated with BRCA1/2 mutations after stratifying by sex or age, although the risk estimates in age-stratified analyses suggested that BRCA1/2 mutation carriers might be more likely to develop colorectal cancer at a younger age.
Our results suggest that a family history of breast cancer is unlikely to be a strong risk factor for colorectal cancer, because a family history of breast cancer in a first-degree female relative was not associated with the risk of colorectal cancer. A large study by Slattery and Kerber (12) identified a weak, but statistically significant, increase in the risk of colorectal cancer given a family history of breast cancer. The confidence intervals that we report in this article encompass the point estimates reported by Slattery and Kerber (12); therefore, we cannot exclude a weak association between a family history of breast cancer and the risk of colorectal cancer.
Previous studies have suggested that the APC polymorphism I1307K might be a low-penetrance susceptibility allele for breast cancer and should be considered a potential confounder of the putative associations between BRCA1/2 mutations or a family history of breast cancer and the risk of colorectal cancer. In one study (17), APC I1307K carriers were more likely than non-carriers to have first-degree relatives with breast cancer, even after adjusting for BRCA1/2 founder mutation carrier status (OR = 1.4, 95% CI = 1.1 to 1.8). A large case series of Ashkenazi Jewish women with breast cancer found that the frequency of APC I1307K was higher among unselected Ashkenazi Jewish case patients with breast cancer than among Ashkenazi Jewish control subjects (18). In our study, APC I1307K did not appear to confound the relationships between colorectal cancer and BRCA1/2 founder mutations or a family history of breast cancer.
In our kincohort analyses, the cumulative risk of all cancers except breast and ovarian was statistically significantly greater in the first-degree relatives of BRCA1/2 mutation carriers than in the first-degree relatives of non-carriers. The statistically significant increase in risk is largely attributable to endometrial cancers, some of which may represent misclassified ovarian cancers because cancer diagnoses in relatives were not histologically confirmed.
Limitations of this study include underreporting and potential misclassification of family histories, possible ascertainment bias, and limited power to precisely measure smaller relative risks that are potentially important. Family history reports of affected relatives could not be confirmed and are likely to be imperfect. However, previous methodologic studies (19,20) have shown good correspondence between reported family histories of cancer and histologically confirmed diagnoses in first-degree relatives. A study from Utah (19) compared self-reported and database-linked family cancer histories to measure the accuracy of family history reporting in casecontrol studies; this study (19) found high sensitivities for breast (83%) and colorectal cancer (73%), with no consistent differences observed between case patients and control subjects. That study suggested that participants in casecontrol studies are able to report family histories of breast or colorectal cancer without observable recall bias, suggesting that underreporting and misclassification of family history in our study is likely to be nondifferential and would, therefore, attenuate any measured associations. Selection bias might exist if case patients chose to participate in our study because of a family history of cancer, especially breast or ovarian cancer. Because it was determined in two prior casecontrol studies (21,22) of breast cancer that case patients and control subjects did not differentially participate in research because of a family history of cancer, any participation bias would likely be nondifferential, again biasing our results toward the null. Given the sample size of 999 case patients and 1028 control subjects with BRCA1/2 genotyping data and a two-sided statistical significance level of = .05, our study achieved 73% power to detect a twofold increased risk of colorectal cancer associated with BRCA1/2 founder mutations, if we assume a BRCA founder mutation prevalence estimate of 2% within the Ashkenazi Jewish study participants. With the same sample size and statistical significance level, our casecontrol study provided 98.9% power to describe a twofold increase in the risk of colorectal cancer associated with a family history of breast cancer in a first-degree female relative. For this power calculation, the prevalence of a positive family history of breast cancer in a first-degree female relative was estimated at 5.8% in the Molecular Epidemiology of Colorectal Cancer control population.
Further research into BRCA mutations and a family history of breast cancer as independent risk factors for colorectal cancer may elaborate the contributions of rare inherited syndromes to the risk of both cancers. MuirTorre syndrome, a variant form of hereditary nonpolyposis colorectal cancer, has been suggested to confer an increased risk of breast cancer, especially after menopause (23). PeutzJeghers syndrome is associated with an increased risk of breast and intestinal cancers (24) and, similarly, the phenotypic spectrum of cancer syndromes associated with the PTEN gene (for example, Cowden syndrome) demonstrates an increased risk of breast cancer and intestinal neoplasia (25). Therefore, it would be reasonable to consider a number of candidate genes in future analyses of genetic variation and the familial aggregation of breast and colorectal cancer.
To date, there is no consensus regarding whether BRCA1/2 mutations increase the risk of colorectal cancer. Although our study does not entirely resolve this controversy, it does provide evidence that Ashkenazi BRCA1/2 founder mutations are not associated with a clinically meaningful or statistically significantly increased risk of colorectal cancer. Furthermore, this study suggests that a family history of breast cancer is not associated with a strong risk of colorectal cancer and that any increased risk of colorectal cancer associated with a family history of breast cancer is unlikely to be mediated by BRCA1 or BRCA2. For BRCA1/2 mutation carriers, enhanced screening for colorectal cancer beyond the guidelines for the general population is not yet supported by the data.
![]() |
NOTES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Supported in part by Public Health Service grants RO1-CA81488 (from the National Cancer Institute to S. B. Gruber), T32 GM07863 (from the National Institute of General Medicine Sciences to B. L. Niell), and T32 HG00040 (from the National Center for Human Genome Research to B. L. Niell), from the National Institutes of Health, Department of Health and Human Services.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1 Ford D, Easton DF, Bishop DT, Narod SA, Goldgar DE. Risks of cancer in BRCA1-mutation carriers. Breast Cancer Linkage Consortium. Lancet 1994;343:6925.[ISI][Medline]
2 Cancer risks in BRCA2 mutation carriers. The Breast Cancer Linkage Consortium. J Natl Cancer Inst 1999;91:13106.
3 Risch HA, McLaughlin JR, Cole DE, Rosen B, Bradley L, Kwan E, et al. Prevalence and penetrance of germline BRCA1 and BRCA2 mutations in a population series of 649 women with ovarian cancer. Am J Hum Genet 2001;68:70010.[CrossRef][ISI][Medline]
4 Thompson D, Easton DF; Breast Cancer Linkage Consortium. Cancer incidence in BRCA1 mutation carriers. J Natl Cancer Inst 2002;94:135865.
5 Brose MS, Rebbeck TR, Calzone KA, Stopfer JE, Nathanson KL, Weber BL. Cancer risk estimates for BRCA1 mutation carriers identified in a risk evaluation program. J Natl Cancer Inst 2002;94:136572.
6 Burke W, Petersen G, Lynch P, Botkin J, Daly M, Garber J, et al. Recommendations for follow-up care of individuals with an inherited predisposition to cancer. I. Hereditary nonpolyposis colon cancer. Cancer Genetics Study Consortium. JAMA 1997;277:9159.[Abstract]
7 Struewing JP, Hartge P, Wacholder S, Baker SM, Berlin M, McAdams M, et al. The risk of cancer associated with specific mutations of BRCA1 and BRCA2 among Ashkenazi Jews. New Engl J Med 1997;336:14018.
8 Drucker L, Stackievitz R, Shpitz B, Yarkoni S. Incidence of BRCA1 and BRCA2 mutations in Ashkenazi colorectal cancer patients: preliminary study. Anticancer Res 2000;20:55961.[ISI][Medline]
9 Chen-Shtoyerman R, Figer A, Fidder HH, Rath P, Yeremin L, Bar Meir S, et al. The frequency of the predominant Jewish mutations in BRCA1 and BRCA2 in unselected Ashkenazi colorectal cancer patients. Br J Cancer 2001;84:4757.[CrossRef][ISI][Medline]
10 Phipps RF, Perry PM. Familial breast cancer and the association with colonic carcinoma. Eur J Surg Oncol 1989;15:10911.[ISI][Medline]
11 Nelson CL, Sellers TA, Rich SS, Potter JD, McGovern PG, Kushi LH. Familial clustering of colon, breast, uterine, and ovarian cancers as assessed by family history. Genet Epidemiol 1993;10:23544.[ISI][Medline]
12 Slattery ML, Kerber RA. Family history of cancer and colon cancer risk: the Utah Population Database [published erratum appears in J Natl Cancer Inst 1994;86:1802]. J Natl Cancer Inst 1994;86:161826.[Abstract]
13 Abeliovich D, Kaduri L, Lerer I, Weinberg N, Amir G, Sagi M, et al. The founder mutations 185delAG and 5382insC in BRCA1 and 6174delT in BRCA2 appear in 60% of ovarian cancer and 30% of early-onset breast cancer patients among Ashkenazi women. Am J Hum Genet 1997;60:50514.[ISI][Medline]
14 Gruber SB. Assay for detecting the I1307K susceptibility allele within the adenomatous polyposis coli gene. In: Killeen AA, editor. Methods in molecular medicine. Totowa (NJ): Humana Press; 2001. p. 26370.
15 Wacholder S, Hartge P, Struewing JP, Pee D, McAdams M, Brody L, et al. The kin-cohort study for estimating penetrance. Am J Epidemiol 1998;148:62330.[Abstract]
16 Moslehi R, Chu W, Karlan B, Fishman D, Risch H, Fields A, et al. BRCA1 and BRCA2 mutation analysis of 208 Ashkenazi Jewish women with ovarian cancer. Am J Hum Genet 2000;66:125972.[CrossRef][ISI][Medline]
17 Woodage T, King SM, Wacholder S, Hartge P, Struewing JP, McAdams M, et al. The APCI1307K allele and cancer risk in a community-based study of Ashkenazi Jews. Nat Genet 1998;20:625.[CrossRef][ISI][Medline]
18 Redston M, Nathanson KL, Yuan ZQ, Neuhausen SL, Satagopan J, Wong N, et al. The APCI1307K allele and breast cancer risk. Nat Genet 1998;20:134.[CrossRef][ISI][Medline]
19 Kerber RA, Slattery ML. Comparison of self-reported and database-linked family history of cancer data in a case-control study. Am J Epidemiol 1997;146:2448.[Abstract]
20 Love RR, Evans AM, Josten DM. The accuracy of patient reports of a family history of cancer. J Chronic Dis 1985;38:28993.[ISI][Medline]
21 Seybolt LM, Vachon C, Potter K, Zheng W, Kushi LH, McGovern PG, et al. Evaluation of potential sources of bias in a genetic epidemiologic study of breast cancer. Genet Epidemiol 1997;14:8595.[CrossRef][ISI][Medline]
22 Madigan MP, Troisi R, Potischman N, Brogan D, Gammon MD, Malone KE, et al. Characteristics of respondents and non-respondents from a case-control study of breast cancer in younger women. Int J Epidemiol 2000;29:7938.
23 Anderson DE. An inherited form of large bowel cancer: Muirs syndrome. Cancer 1980;45(5 Suppl):11037.[ISI][Medline]
24 Giardiello FM, Brensinger JD, Tersmette AC, Goodman SN, Petersen GM, Booker SV, et al. Very high risk of cancer in familial Peutz-Jeghers syndrome. Gastroenterology 2000;119:144753.[ISI][Medline]
25 Eng C. Will the real Cowden syndrome please stand up: revised diagnostic criteria. J Med Genet 2000;37:82830.
Manuscript received July 1, 2003; revised November 3, 2003; accepted November 13, 2003.
This article has been cited by other articles in HighWire Press-hosted journals:
Correspondence about this Article
Editorial about this Article
![]() |
||||
|
Oxford University Press Privacy Policy and Legal Statement |