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1 H. Lee Moffitt Cancer Center and Research Institute, and 2 Department of Interdisciplinary Oncology, College of Medicine, University of South Florida, Tampa, Florida; and 3 All Children's Hospital, Department of Pediatrics, College of Medicine, University of South Florida, St. Petersburg, Florida
Requests for reprints: Jenny Permuth-Wey, Lifetime Cancer Screening and Prevention Center, H. Lee Moffitt Cancer Center and Research Institute, 4117 East Fowler Avenue, Tampa, FL 33617. Phone: 813-979-6770; Fax: 813-558-4807. E-mail: permutjm{at}moffitt.usf.edu
| Abstract |
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3% of individuals undergoing BRCA1/BRCA2 testing reported African American ancestry. Data from previous studies show that among African American women a greater proportion of breast cancer cases are diagnosed at age <45 years in comparison with Caucasians. Because breast cancer occurring at a young age is one of the hallmarks of high penetrance genes, the prevalence, spectrum, and effects of BRCA1/BRCA2 mutations may differ substantially between African Americans and Caucasians, and further investigation is warranted.
We conducted a hospital-based study of African American breast cancer patients with early age at diagnosis (
45 years) or family history of breast or ovarian cancer. We identified four deleterious mutations in BRCA1 or BRCA2 among the 10 families tested, of which two were novel BRCA2 mutations, one was the west African founder mutation (BRCA1 943ins10), and one was a recurrent mutation that may be a candidate for a second African American founder mutation (BRCA1 IVS13+1G>A). Our results support previous data in demonstrating that (a) the spectrum of mutations among African Americans is unique, (b) family history of breast cancer is an important predictor of hereditary cancer susceptibility among African Americans, and (c) empirical data may be useful in estimating mutation risk among African Americans.
| Introduction |
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Overall, 5% to 10% of breast and ovarian cancer cases are due to mutations in BRCA1 and BRCA2 (7, 8). However, most studies of BRCA1 and BRCA2 have been done in Caucasian families with a strong history of breast cancer. The spectrum of mutations identified in the U.S. population thus far reflects mostly European migrations to North America. The spectrum of mutations in the African American population is slowly beginning to be characterized.
A few genetic studies have included African American women from breast cancer families unselected for ethnic background (9-12). As of November 2001, according to data from Myriad Genetic Laboratories, Inc., an estimated 308 African American individuals had undergone BRCA1 and BRCA2 testing (compared with
9,500 Caucasians), of whom 52 had deleterious mutations (13). Twenty-six of the 52 mutations had been observed in only one family.
Newman et al. suggested that the incidence of BRCA1 mutations might be lower among breast cancer patients of African American ancestry. They conducted a population-based study including 99 African American women with breast cancer and identified no disease-related BRCA1 mutations in any of these women (12). However, no details regarding family history or age at diagnosis were specified. Recently, a study of 45 high-risk African American women identified only two deleterious BRCA1 mutations (14).
A few studies have exclusively investigated inherited breast cancer in African American women and most have evaluated only BRCA1 (14-18). The results from these studies indicate that founder mutations are present in the African American population and additional studies are needed to determine their prevalence. Mefford et al. (14) reported three novel BRCA1 mutations in African Americans, with one of these mutations (943ins10) identified in two unrelated families in the series. This mutation has now been reported in other families from Washington (DC), Florida, South Carolina, Bahamas, and the Ivory Coast, suggesting that it is an ancient African founder mutation (18, 19). More recently, in a hospital-based series from Nigeria, three novel mutations in BRCA1 were reported in 70 young African women with breast cancer screened for BRCA1 and BRCA2 (15). A recent clinic-based sample of 28 African American families with breast cancer identified five deleterious BRCA1 or BRCA2 mutations, four of which were novel (17). Hence, data from several groups support the existence of a distinct spectrum of BRCA1 and BRCA2 mutations in African Americans. Further study is needed to examine the contribution of these mutations to the disproportionate number of cases occurring at a young age in this population.
To further characterize the role of BRCA1 and BRCA2 among African American breast cancer patients, we did a hospital-based study using full gene sequencing of BRCA1 and BRCA2.
| Materials and Methods |
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45 years or (b) reported family history of breast/ovarian cancer. There were 58 women identified, of whom 26 could be contacted. Patients were invited to participate in the study through their treating physician. Of 26 potential participants who could be contacted, 10 (38%) individuals enrolled in the study. Participants consisted of patients who were scheduled for follow-up appointments at the Moffitt Cancer Center. Patients no longer receiving follow-up care at the Moffitt Cancer Center indicated they were unwilling to travel to the center to participate. All study participants obtained genetic counseling and gave informed consent prior to blood drawing in accordance with the protocol approved by the institutional review board of the University of South Florida. Funding for the study covered all costs including genetic counseling and testing. During the genetic counseling appointment, family history details were obtained including current age, age at diagnosis of cancer, and site (and where possible, histologic type) of cancer in three generations. Family history information was taken as that reported by the proband, as medical record verification of cancer in family members was not possible. Studies suggest that the diagnosis of cancer reported in relatives is likely to be accurate at least for first-degree relatives (20-22).
Risk assessment models used to estimate the likelihood of a mutation for all families included BRCAPRO (23) and the updated Myriad 2002 data (13). Mutation analysis in 9 of the 10 participants was done by Myriad Genetic Laboratories according to published protocol (13). Complete sequencing of the coding regions and flanking intron/exon boundaries was done. One analysis was done by OncorMed (Gaithersburg, MD) by alternate methodology. All participants chose to be informed of their genetic test results.
| Results |
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Our analysis would not have identified large deletions, noncoding region BRCA1 and BRCA2 mutations, or other unidentified genes that may explain early age at diagnosis or familial clustering of breast cancer in the remaining families.
Risk Assessment
Risk assessment using BRCAPRO (23) and Myriad Genetic Laboratories empirical data (13) was done for each family (Table 2).
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DNA Testing Results
Results of the DNA analysis showed that 4 of the 10 participants were mutation carriers, of whom 2 carried BRCA1 mutations and 2 carried BRCA2 mutations (Table 3).
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In addition, four variants of uncertain significance were identified (Table 3) in a total of three patients. The variants reported in our study have all been seen previously by Myriad Genetic Laboratories; however, their pathogenicity remains to be determined.
Tumor Histology
The histology reports for all mutation carriers were reviewed. The two BRCA1 carriers had estrogen receptor and progesterone receptornegative tumors and the two BRCA2 carriers had estrogen receptor and progesterone receptorpositive tumors.
| Discussion |
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Studies in Caucasians show that BRCA1 mutations contribute to more cases of early-onset breast cancer than do BRCA2 mutations (30), with the average age of breast cancer in BRCA1 and BRCA2 carriers being 40 and 45 years, respectively (31). In our study, the average age of breast cancer diagnosis in BRCA1 and BRCA2 carriers was 33 and 39 years, respectively, suggesting a similar trend; however, our numbers are too small to draw firm conclusions.
Based on recent studies, the BRCAPRO risk assessment model has been verified as an adequate predictor of BRCA1/BRCA2 mutation carrier status in Caucasians (32, 33). This model adequately predicted mutation carrier status of African American women in our study. Because the Myriad "model" is based on empirical data (primarily in Caucasians), it is likely to be an adequate predictor of mutation carrier status, which was also seen in this study. Hence, our data suggest that the same risk assessment models may be useful in prediction of carrier status of African Americans and Caucasians.
The spectrum of mutations seen in African Americans seems to be distinct from that seen in Caucasians (14-18, 34). Of the four deleterious mutations identified through our study, two mutations were novel. One mutation was the African American founder mutation, BRCA1 943ins10 (14, 18, 19). The fourth mutation (IVS13+1G>A) is a recurrent mutation and a candidate for being a second African American founder mutation.
Founder mutations, rather than mutation hotspots, are seen in certain ethnic subpopulations and are responsible for the increased frequencies of some mutations. Such founder mutations have been described in families from ethnic groups that were geographically or culturally isolated including Ashkenazi Jews (35), Icelandics (36), French Canadians (37), and Filipinos (38) as well as several other population groups. The benefits of identifying founder mutations in population groups include the ability to target testing to the founder mutations, allowing for a more rapid and inexpensive test. Among individuals of African ancestry, only one founder mutation (BRCA1 943ins10) has been identified previously and confirmed through haplotype analysis (14, 18, 19), which is necessary to establish founder mutations. The family in our study with this mutation reported west African ancestry, which is consistent with previously reported families with this mutation.
One patient in our study had the BRCA1 IVS13+1G>A splice-site mutation, a recurrent mutation seen 10 times previously, according to Myriad Genetic Laboratories5 (although only six of these mutations have been reported in the Breast Cancer Information Core database; ref. 25); 6 of the 10 patients reported African Americans ethnicity. This mutation may represent a second African American founder mutation; however, haplotype analysis is required for confirmation.
The unclassified variants reported in our study have all been seen previously by Myriad Genetic Laboratories; however, their pathogenicity remains to be determined. The difficulties in interpreting unclassified variants, magnified in minority groups by the lack of clinical data, will likely continue until further study of these groups is accomplished. This highlights the need for development of functional assays for BRCA1 and BRCA2.
Previous studies in Caucasians have indicated that breast cancer tends to be estrogen and progesterone receptor negative in BRCA1 carriers and tends to be estrogen and progesterone receptor positive in BRCA2 carriers (39, 40), which was consistent with that seen in our African American study population. We hypothesize that if tumor characteristics in African American and Caucasian BRCA1/BRCA2 carriers are similar, this highlights the predominant role of BRCA1/BRCA2 in hereditary tumorigenesis and suggests that other factors, which vary by race, may have a lesser role.
The limitations of this study included a small sample size, despite attempts to enhance recruitment. The patients were approached through an African American study coordinator and were offered genetic counseling and full BRCA1/BRCA2 gene sequencing at no cost. Patients declined participation unless they were already planning a trip to the Moffitt Cancer Center for follow-up. Interest in study participation for African Americans has generally been reported as low (41), which was also seen in our study. Potential participants were identified through the Moffitt Cancer Registry, which records family history data reported by the proband. Another limitation of the study was that there was no verification of family history information, which was attempted through the cancer registry at the Moffitt Cancer Center.
Information about the role of the BRCA1 and BRCA2 genes in hereditary susceptibility to breast and ovarian cancer in African American families is limited. Data from this study add to the limited information available about (a) incidence and types of mutations, furthering the knowledge about founder mutations, and (b) family history factors and tumor characteristics among African Americans at risk for inherited breast and ovarian cancer susceptibility.
It is of interest that although the study was relatively small and only four mutations were identified, one of the mutations is a previously identified founder mutation and another one is a recurrent mutation and a candidate for a second founder mutation. Targeted efforts to define the spectrum and penetrance of BRCA1 and BRCA2 mutations in this ethnic group are warranted. We and others are continuing such efforts that will lead to more accurate risk assessment and more effective cancer control initiatives among African American women at high risk for breast and ovarian cancer.
| Acknowledgments |
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| Footnotes |
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
4 Myriad Genetic Laboratories, unpublished data. ![]()
Received 2/10/04; accepted 5/10/04.
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