Why is distinguishing germline from somatic BRCA mutations clinically important?

• A. Germline BRCA mutations affect family risk and cascade testing; somatic BRCA mutations guide tumor-targeted therapy but do not imply inherited risk.
• B. Somatic BRCA mutations have no impact on therapy.
• C. There is no difference clinically.
• D. Germline mutations have no family implications.

Answer: (A)

BRCA mutations can be present in every cell or just in the tumor, and that distinction changes both how we think about cancer risk for relatives and how we treat the cancer itself. A germline BRCA mutation is inherited and found in all cells, so it carries implications for family members. This means relatives may also carry the mutation and could benefit from genetic counseling, targeted surveillance, risk-reducing strategies, or early detection for cancers associated with BRCA1/2. In contrast, a somatic BRCA mutation is confined to the tumor tissue and does not by itself indicate inherited risk for family members, so it doesn’t automatically prompt cascade testing.

Therapeutically, tumor BRCA status matters because tumors with BRCA deficiency often rely on defective DNA repair and can be particularly sensitive to PARP inhibitors or platinum-based chemotherapy. Thus, identifying a BRCA mutation in the tumor helps tailor treatment, regardless of whether the mutation is germline or somatic. If a mutation is found in the tumor, confirming whether it is germline is important for counseling relatives and for assessing the patient’s overall inherited cancer risk; if it’s somatic only, relatives aren’t automatically at increased inherited risk, though the tumor still might respond to targeted therapy based on its BRCA status.