An unusual BRCA mutation distribution in a high risk cancer genetics clinic

The Database of Individuals at High Risk for Breast, Ovarian, or Other Hereditary Cancers at the Arizona Cancer Center in Tucson, Arizona assesses cancer risk factors and outcomes in patients with a family history of cancer or a known genetic mutation. We analyzed the subset of clinic probands who carry deleterious BRCA gene mutations to identify factors that could explain why mutations in BRCA2 outnumber those in BRCA1. Medical, family, social, ethnic and genetic mutation histories were collected from consenting patients' electronic medical records. Differences between BRCA1 and BRCA2 probands from this database were analyzed for statistical significance and compared to published analyses. A significantly higher proportion of our clinic probands carry mutations in BRCA2 than BRCA1, compared with previous reports of mutation prevalence. This also holds true for the Hispanic sub-group. Probands with BRCA2 mutations were significantly more likely than their BRCA1 counterparts to present to the high risk clinic without a diagnosis of cancer. Other differences between the groups were not significant. Six previously unreported BRCA2 mutations appear in our clinic population. The increased proportion of probands carrying deleterious BRCA2 mutations is likely multifactorial, but may reflect aspects of Southern Arizona's unique ethnic heritage.