Study: Prevalence of BRCA mutations in Bahamian women

IN-DEPTH REVIEW OF RESEARCH

Study background:

The Bahamas has the highest prevalence of BRCA mutations among breast cancer patients.  In one study, one of the six BRCA1 founder mutations was identified in 49 (23%) of 214 unselected Bahamian breast cancer patients. In a follow-up to this study, researchers conducted full sequencing for BRCA1 and BRCA2 for the 156 patients who did not have a known BRCA1 founder mutation. Four of these patients were found to have a novel founder mutation in BRCA2; five other unique mutations in BRCA1 and BRCA2 were also identified. In total, mutations were discovered in 58 of the 214 patients (27%). This prevalence far exceeds that of any other population.

In comparison, the reported BRCA prevalence in Ashkenazi Jewish women is between 1% and 2% , with three known founder mutations accounting for the majority of BRCA mutations in this population. NCCN guidelines recommend testing for unselected Jewish women who have a personal history of breast cancer.  Many genetics experts believe that the high prevalence of BRCA mutations in Jewish women and the ability to test for specific founder mutations makes population-based screening cost effective. (It is important to note that not all women with a BRCA mutation have a family history of breast and/or ovarian cancer.  This is especially true for women with a limited number of female relatives.)

Because the prevalence of BRCA mutations among breast cancer patients in the Bahamas is higher than any other population, researchers sought to determine whether population-based testing is an effective approach to BRCA testing in the Bahamas. 

Researchers of this study wanted to know:

If they could generate evidence to help inform an effective BRCA testing policy for Bahamian women.

Population(s) looked at in the study:

These researchers screened a large sample of Bahamian women with no personal history of breast or ovarian cancer. These included both women with and women without a family history of cancer.

Personal and family histories of cancer were collected during pre-test genetic counseling.

A total of 1,921 unaffected Bahamian women provided a saliva sample from which DNA was isolated.  Of these women, 44 were not screened for one of the seven founder mutations due to low quality DNA; 30 other participants were excluded because their family cancer history was unknown.

Study findings: 

A total of 1,847 unaffected Bahamian women underwent genetic testing:

• Among the 705 (38.2%) women who reported having a family history of breast and/or ovarian cancer, 20 (2.8%) had a BRCA mutation.
   
• Among the 1,089 women who reported no personal or familial history of breast and/or ovarian cancer, only one (0.09%) had a BRCA mutation.
   
• Among the 53 women who reported having a relative with a Bahamian BRCA founder mutation, 20 (37.7%) had a BRCA mutation.
   
• 41 BRCA mutations were identified.

In this study, 2.8% of women with a first- or second- degree relative with breast or ovarian cancer had a Bahamian founder mutation.

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Limitations:

The patients in this study-mostly were employees of a large resort-were self-selected and did not represent a random sample. Participants were asked about their Bahamian ancestry, however, this information was not verified. Finally, testing in this study was limited to the seven Bahamian founder mutations; participants may have had other deleterious BRCA mutations.

Conclusions:

The results of this study support a policy to extend genetic testing for the seven Bahamian BRCA1 and BRCA2 founder mutations to all Bahamian women with a family history of breast or ovarian cancer. 

It is important to note that unaffected Bahamian women without a family history of breast or ovarian cancer rarely have a BRCA mutation (0.09% in this study). It is unclear why the prevalence of mutations in unselected breast cancer patients would be so high compared to a relatively low prevalence in the general population. 

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Posted 3/4/19

References

Trottier M, Lunn J, Butler R, Curling D, Turnquest T, Francis W, Halliday D, Royer R, Zhang S, Li S, Thompson I, Donenberg T, Hurley J, Akbari MR, and Narod SA. Prevalence of founder mutations in the BRCA1 and BRCA2 genes among unaffected women from the Bahamas. Clinical Genetics 2016. 89(3):328-31.

Akbari MR, Donenberg T, Lunn J, Curling D, Turnquest T, Krill-Jackson E, Zhang S, Narod SA, and Hurley J. The spectrum of BRCA1 and BRCA2 mutations in breast cancer patients in the Bahamas. Clinical Genetics. January, 2014. 85(1): 64-67.

Donenberg T, Lunn J, Curling D, Turnquest T, Krill-Jackson E, Royer R, Narod SA, and Hurley J. A high prevalence of BRCA1 mutations among breast cancer patients from the Bahamas. Breast Cancer Research and Treatment. 2011. 125(2):591-6.