BRCA1 [BReast CAncer gene 1] and BRCA2 [BReast CAncer gene 2] are genes that produce proteins that help repair damaged DNA. everyone has two copies of each of these genes—inherited from each parent and despite what their names suggest, BRCA1 and BRCA2 do not cause breast cancer, but are rather are tumour suppressor genes – repairing DNA breaks that can lead to cancer.
there are two ways that cancer can develop from the BRCA gene – a harmful variant from the BRCA gene can be inherited at birth from one parent – this is called a germline mutation [see our post here to better understand germline and somatic mutations]. because you inherit two copies of the BRCA gene – one from each parent, there is a 50% chance of inheriting a harmful variant.
The other way cancer develops is from somatic mutations – these changes are acquired – changes occur to the DNA throughout the person’s lifetime and are either due to mistakes when the DNA is copied or as the result of environmental factors [such as UV exposure].
BRCA genes have been shown to be associated with an increased risk of various cancers including breast cancer [in women and men], ovarian, prostate, pancreatic, gastrointestinal and colorectal cancers.
BRCA mutations can also be used to guide clinical decision making – predicting response to treatment with certain therapies in certain cancers.