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Molecular Oncology, Markers, Clinical Correlates |
Memorial Sloan-Kettering Cancer Center, New York, New York 10021 [J. M. S., J. B., N. D. K., M. R., L. S., K. O.], and The Center for Research on Womens Health, Toronto, Ontario, Canada [S. N.]
| ABSTRACT |
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Experimental Design: A total of 382 ovarian cancer cases self-identified as being Jewish with no prior diagnosis of breast cancer were derived from two hospital-based series. In the first series, all 197 invasive epithelial ovarian cancer cases self-identified as Jewish and without a prior history of breast cancer, diagnosed and treated at Memorial Sloan-Kettering Cancer Center between 1986 and 2000, were identified. In the second series, 185 Jewish invasive epithelial ovarian cancer patients without prior breast cancer were identified in a study conducted at 11 centers in North America and Israel from 1995 to 1996. Controls were 3434 Jewish women without any prior history of breast or ovarian cancer from a large study of genotyped volunteers of Jewish origin in the Washington, D. C. area recruited by investigators at the National Cancer Institute. The cases and controls were genotyped for three Ashkenazi Jewish founder mutations, namely 185delAG and 5382insC in BRCA1 and 6174delT in BRCA2. The lifetime penetrances were estimated using the odds ratios, mutation prevalence in the controls, and ovarian cancer incidence rates in the general American population obtained from the Surveillance, Epidemiology and End Results database adjusted for the incidence of ovarian cancer following breast cancer.
Results: Mutations were identified in 147 cases and 62 controls. The estimated penetrances at age 70 years were 37% (95% confidence interval, 2571%) for a BRCA1 mutation and 21% (95% CI, 1341%) for a BRCA2 mutation.
Conclusions: The lifetime penetrances of BRCA1 mutations are lower than estimates obtained using familial data with multiple affected members but larger than estimates from some population-based proband series. The lifetime penetrance estimate of a BRCA2 mutation is in the range reported by some of the studies based on familial data. These results could have implications for clinical counseling, surgical interventions, and screening recommendations in women carrying these founder mutations.
| INTRODUCTION |
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In studies involving family-based ascertainment, families with a high cancer incidence are more likely to be identified than families with no or fewer cancers among the relatives of probands. As a result, this can lead to a substantial positive bias in the risk estimates. Even population-based studies that rely on occurrences of cancer in relatives of probands to estimate penetrance can be biased if incident cases are used as probands (10) . We recently used a case-control design to estimate the lifetime risk of breast cancer conferred by inherited BRCA1 and BRCA2 mutations among Ashkenazi Jewish women (11) . In this design familial aggregation is not used, eliminating ascertainment bias. We showed that the lifetime risk of breast cancer due to an inherited mutation is substantially lower than the estimates reported in family-based studies. The goal of this study is to investigate the lifetime risk of ovarian cancer due to an inherited BRCA1 or BRCA2 mutation among Ashkenazi Jewish women ascertained using the same case-control approach and compare the estimates with those obtained by family-based and population-based studies.
| MATERIALS AND METHODS |
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The second series comprised of ovarian cancer cases from 11 centers in North America and Israel, as reported by Moslehi et al. (13) . Ovarian cancer patients, self-reported as Jewish, were contacted to participate in a study of mutation analysis of BRCA1 and BRCA2 genes. A total of 465 ovarian cancer cases of Jewish origin were identified, of whom 208 cases were alive. These 208 individuals were pathologically confirmed to have invasive epithelial ovarian cancer, agreed to participate in the mutation analysis study, and provided blood samples. Twenty-three of these 208 ovarian cancer patients had a prior history of breast cancer.
Aggregating data from these two series gave a total of 436 Ashkenazi Jewish ovarian cancer patients, of whom 382 cases did not have a prior history of breast cancer.
Controls.
The controls required for this study were obtained from a study of genotyped volunteers in the Washington, D. C. area (15)
, providing a large series of Jewish individuals without a history of breast or ovarian cancer at the time of ascertainment. Jewish volunteers, both men and women, were recruited through advertisements. Breast and ovarian cancer history of the volunteers and their families was obtained. Furthermore, blood samples were obtained from all of the volunteers. A total of 3434 women without a personal history of breast or ovarian cancer at the time of data collection were identified for this study. The presence or absence of the three founder mutations was determined for every individual using previously published methods (15)
. Of these 3434 volunteers, a total of 1606 women (47%) had a first- or second-degree relative affected with breast or ovarian cancer.
Statistical Methods.
All analyses were stratified by age. Because breast cancer can be a competing cause of risk for ovarian cancer incidence, inclusion of the 54 ovarian cancer patients with a prior diagnosis of breast cancer may result in biased penetrance estimates. Therefore, penetrance estimates were calculated by restricting the cases to the 382 patients without a prior history of breast cancer. All 3434 controls were included in the analysis. Penetrance estimation calculations are provided in the "Appendix ." This approach is similar to the estimation method described in our breast cancer penetrance study (11)
. Briefly, the lifetime risk in a given age group can be estimated as a function of the following three quantities: (a) SEER ovarian cancer incidence rate after adjusting for the SEER incidence of ovarian cancer in patients with a prior diagnosis of breast cancer in that age group, and the SEER breast cancer incidence in that age group; (b) the age-specific relative risk of the mutation; and (c) the age-specific carrier prevalence of the mutation. This calculation involves the following three assumptions: (a) the hospital-based series of Jewish ovarian cancer cases are representative of the general population series of Jewish cases; (b) the controls are representative of the general Jewish population; and (c) the breast and ovarian cancer incidence rates among the Jewish population without BRCA mutation is similar to the SEER breast and ovarian cancer incidence rate. The CIs of the lifetime risk estimates were calculated using the bootstrap method (16)
. This involves repeatedly calculating penetrance estimates by sampling cases and controls with replacement from the observed data and deriving the CIs from the empirical distribution of the penetrance estimates.
The risk conferred by BRCA1 versus BRCA2 mutations and the risk conferred by 185delAG versus 5382insC BRCA1 mutations were compared using a logistic regression model restricted to mutation carriers (11) . The outcome was case-control status. The variables entered into the model were the mutation BRCA1 versus BRCA2 (or 185delAG versus 5382insC) and age. A likelihood ratio test was then used to test the hypothesis of no difference in the risk conferred by the two mutations.
| RESULTS |
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50 age group. The corresponding relative risks due to an inherited BRCA2 mutation were estimated as 6.5, 14.9, and 29.7, respectively.
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| DISCUSSION |
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The lifetime risks were estimated based on three major assumptions: (a) the hospital-based cases are representative of the population of ovarian cancer cases; (b) the volunteer controls are representative of the general Ashkenazi Jewish population; and (c) the cancer incidence in the general Ashkenazi Jewish population without BRCA mutations is similar to the SEER rate. The cases were derived from a hospital-based series of ovarian cancer patients. Because initial management of ovarian cancer in the United States is predominantly surgical, cases from the MSKCC series are likely to be similar to the general ovarian cancer case population in the United States. Furthermore, previous analysis showed that the clinicopathological features of high-risk (i.e., BRCA-linked) cancer patients diagnosed and treated at MSKCC were similar to those of sporadic ovarian cancer cases (12) . The controls were derived from a series of volunteers recruited via both general and Jewish-targeted media outlets. It is likely that individuals with a strong family history were more likely to participate in a study analyzing genetic influence on cancer risk. If the control group contained an enriched proportion of mutation carriers, then the odds ratios derived in our analysis would be underestimates, and the true penetrance figures would actually be higher. A total of 62 (1.8%) controls had a BRCA1 or BRCA2 mutation. This mutation frequency is similar to the 2.2% reported in the study of general Ashkenazi Jewish population (17) , suggesting that the mutation prevalence is not inflated among these controls. The SEER ovarian cancer incidence rates were assumed to the represent ovarian cancer incidence among the general Jewish population and the incidence of second primary ovarian cancer following a first primary breast cancer. Violation of this assumption would lead to biased risk estimates. Therefore, a sensitivity analysis was performed to determine lifetime risk when the Jewish population had 10% higher risk than the SEER population. The lifetime risk at age 70 years increased to 40% for a BRCA1 mutation and to 23% for a BRCA2 mutation.
Gayther et al. (18) reported a correlation between the location of a truncating mutation in the BRCA1 coding region and the chances of developing breast or ovarian cancer using data from 60 families. Mutations near the 5' end of the coding region are thought to confer a higher risk than mutations near the 3' end. The 185delAG mutation is located near the 5' end, and the 5382insC mutation is located near the 3' end of the BRCA1 coding region. Our estimate of a higher penetrance associated with a 185delAG mutation than a 5382insC mutation, although not statistically significant, is consistent with these findings.
The penetrance of BRCA2 mutation has not been widely reported. Our results show that a BRCA2 mutation is not a significant risk factor in younger women (age <40 years; odds ratio, 6.5; 95% CI, 0.855.6). The odds ratio increases as the population ages, suggesting BRCA2 to be a risk factor only in older women. The 6174delT mutation is located in the OCCR (19) , in the region of exon 11 extending from nucleotide 3035 to 6629. Truncating mutations in OCCR are known to be associated with an increased risk of breast and ovarian cancer (5 , 19) . Furthermore, founder mutations in BRCA1 are believed to have a significantly higher penetrance than a founder mutation in BRCA2 (20) . Our results are consistent with the findings of these published studies. Recent studies have reported associations between other cancers such as colorectal, stomach, pancreatic, and prostate cancers and mutations in BRCA1 and OCCR BRCA2 mutations (2 , 5 , 9 , 13 , 21 , 22) .
Our penetrance estimates can have implications for the management of ovarian cancer in germ-line mutation carriers. Prophylactic mastectomy and oophorectomy may be reasonable options for germ-line BRCA1 and BRCA2 mutation carriers. Their advantages have been reported in recent literature (23, 24, 25, 26) . The penetrance estimates derived in this study can be used in decisions regarding such preventive measures (i.e., risk-reducing oophorectomy might safely be delayed until after menopause in carriers of the 6174delT BRCA2 mutation). Surgical removal of the ovaries is increasingly offered to BRCA mutation carriers, given the variable sensitivity of ovarian cancer screening strategies and the finding of early stage tumors in "prophylactic" oophorectomy specimens (27) . In the absence of more sensitive means of detecting ovarian cancer, penetrance estimates such as those provided here will continue to be used to inform surgical as well as medical interventions in populations at greatest hereditary risk for ovarian cancer.
| Appendix 1 |
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The age-specific carrier incidence in the ath age group, Ia0, can be calculated as a function of the following three quantities: (a) the general population incidence rate of ovarian cancer without a prior history of breast cancer in the ath age group, denoted Ra* (referred to as the age-specific adjusted ovarian cancer incidence rate); (b) the age-specific mutation prevalence, denoted
a; and (c) the age-specific relative risk of the mutation, denoted
a.
The overall incidence of ovarian cancer for a given age group in the general population is the weighted average of ovarian cancer incidence with and without a prior history of breast cancer, weighted by the (competing risk of) breast cancer incidence in the general population in that age group. Furthermore, the ovarian cancer incidence among those without a prior history of breast cancer in the general population is a weighted average of the incidence among carriers and noncarriers without breast cancer, weighted by the mutation prevalence. For the ath age group, denote Ia* as the general population incidence of ovarian cancer, Sa* as the incidence of (second primary) ovarian cancer among (first primary) breast cancer cases, and Fa* as the incidence of breast cancer in the general population. Then, the age-specific adjusted ovarian cancer incidence rate is given by:
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| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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1 Supported in part by NIH Grant GM60457. ![]()
2 To whom requests for reprints should be addressed, at Department of Epidemiology and Biostatistics, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10021. Phone: (212) 639-2467; Fax: (212) 717-3137; E-mail: satagopj{at}mskcc.org ![]()
3 The abbreviations used are: SEER, Surveillance, Epidemiology and End Results; CI, confidence interval; MSKCC, Memorial Sloan-Kettering Cancer Center; OCCR, ovarian cancer cluster region. ![]()
Received 3/12/02; revised 7/10/02; accepted 7/16/02.
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