Somatic vs Germline BRCA Mutations: What's the Difference?

When you are diagnosed with ovarian cancer, your care team will likely test for mutations in the BRCA1 or BRCA2 genes. If your test results show a BRCA mutation, it is crucial to know whether that mutation is germline (inherited) or somatic (tumor-only). The main difference is that a germline mutation is present in every cell of your body and can be passed down in families, while a somatic mutation developed only in the cancer cells and is not inherited ^[1][2]. However, both types of mutations make the cancer highly sensitive to certain targeted treatments ^[3].

Somatic vs. Germline: What Do They Mean?

Germline BRCA Mutations
A germline mutation is an inherited change in your DNA ^[2].

• Where it is found: Because you are born with it, the mutation exists in every cell of your body (which is why it is usually tested via a simple blood draw or saliva sample) ^[4].
• Family impact: You inherited this mutation from one of your parents, meaning your blood relatives (such as siblings and children) have a 50% chance of carrying it as well ^[2].
• Future cancer risk: Germline BRCA mutations increase your risk of developing a second primary cancer, such as breast, pancreatic, or skin cancer (melanoma) ^[2][4]. Because of this, you may need additional cancer screenings, like mammograms or breast MRIs, moving forward ^[4].

Somatic BRCA Mutations
A somatic mutation is an acquired change that happens spontaneously ^[1].

• Where it is found: This mutation exists only in your ovarian cancer cells ^[1]. It is usually tested using a sample of the tumor tissue that was already removed during your previous surgery or biopsy, so you typically will not need another procedure for this test.
• Family impact: Somatic mutations are not inherited from your parents and cannot be passed to your children ^[1].
• Future cancer risk: Having a somatic mutation in your ovarian tumor does not increase your risk of developing breast or other cancers in the rest of your body ^[1]. (However, you should still continue your routine, age-appropriate cancer screenings.)

How Does This Affect Your Treatment?

For treating ovarian cancer, somatic and germline BRCA mutations behave very similarly. Both mutations damage the cancer cell’s ability to repair its own DNA ^[5].

Because both types of mutations create this specific weakness in the tumor, both make you an excellent candidate for a type of targeted therapy called PARP inhibitors (poly-ADP ribose polymerase inhibitors) ^[3]. PARP inhibitors (such as olaparib, niraparib, or rucaparib) exploit this DNA repair defect and are designed to help destroy the cancer cells ^[5].

Unlike traditional intravenous chemotherapy, PARP inhibitors are typically taken at home as a daily oral pill. Clinical studies show that maintenance therapy with PARP inhibitors significantly prolongs the time before the cancer grows back, regardless of whether your mutation is germline or somatic ^[6][5]. While highly effective, these medications can cause side effects—such as fatigue, nausea, or low blood counts—so it is important to discuss what to expect with your care team.

Why Comprehensive Testing Matters

Because of these distinct implications for treatment and family risk, modern clinical guidelines recommend comprehensive testing ^[7].

• If only your blood is tested, you might miss a somatic mutation that could make you eligible for a PARP inhibitor.
• If only your tumor is tested and a mutation is found, you will typically need a follow-up blood test to confirm whether that mutation is somatic or germline ^[7][8].

Knowing the exact nature of your mutation empowers both you and your care team to make the most informed choices for your treatment and your family’s future. If a germline mutation is found, speaking with a genetic counselor can provide you and your loved ones with a clear roadmap for managing inherited risk.