In general, both BRCA1 and BRCA2 mutations have been found to increase the lifetime risk of breast cancer very roughly between 50 and 85%. BRCA1 mutations however result in a higher risk of lifetime ovarian cancer (up to 60% in some studies) than BRCA2 (up to 20% in some studies). There is also a predilection for the two mutations to present with different types of cancer with some differences between the sexes. For example, BRCA2 is more likely to produce ER+ (estrogen receptor positive) cancer. It is also (for less than definitive reasons) more likely to cause male breast cancer. BRCA1 is more likely to result in a more aggressive form of breast cancer typically known as "triple negative" breast cancers. Interestingly, prophylactic oophorectomy (removal of ovaries) is effective in decreasing the risk of breast cancer in the setting of a BRCA2 mutation but not BRCA1. This is believed to be the result of decreasing the estrogen levels which could encourage an ER+ breast cancer from BRCA2.
The incidence of BRCA1 and BRCA2 also varies by ethnicity. African Americans are more likely to have BRCA2 mutations while Caucasians are slightly more likely to have a mutation in BRCA1. I hope this helps anyone looking for a concise breakdown of some of the most important differences between these two genes.
-Ryan Polselli, M.D.
Breast Imaging Radiologist
ryan-polselli.com or ryanpolselli.com