Germline vs Somatic: How Mutations Relate to Breast Cancer

If you’ve been told you carry a BRCA1, BRCA2, or other genetic mutation, you might wonder — is it germline or somatic?

Understanding the difference is key to effective cancer prevention and treatment.

1. What is a Germline Mutation?

• Present from birth in reproductive cells (egg or sperm)
• Inherited from parents and passed down to children
• Found in every cell of the body
• Increases risk of various cancers such as breast, ovarian, and pancreatic cancer
• Commonly affected genes include BRCA1, BRCA2, ATM, PALB2

Thai research (Kamdee et al., 2025) found:

• 13% of Thai breast cancer patients had germline mutations
• BRCA1 mutation: 4.8%, BRCA2 mutation: 4.1%
• Mutations in ATM and TP53 were also identified

 Treatment & prevention impact:

• Earlier cancer screening
• Consideration for preventive surgeries
• Better response to PARP inhibitors such as olaparib

2. What is a Somatic Mutation?

• Develops after birth
• Occurs in body (non-reproductive) cells
• Not inherited by children
• Found only in tumor tissue and not in blood
• May be caused by radiation, toxins, or cell replication errors

Thai breast cancer tumor data showed frequent mutations in:

• TP53: Common in HER2+ and TNBC subtypes
• PIK3CA: Common in HR+/HER2-
• HER2 (ERBB2): Found in up to 32%
• GATA3: Found in specific breast cancer subtypes

Treatment impact:

• Targeted therapies such as trastuzumab (HER2+) and capivasertib (PIK3CA pathway)
• Certain mutation combinations (e.g., TP53 + PTEN) may indicate more aggressive disease

3. How Germline and Somatic Mutations Connect

• People with germline BRCA1/2 mutations may accumulate somatic mutations like TP53 more easily
• Cancer development pathways may differ from those without BRCA mutations
• Testing for both types enables more accurate treatment planning and family risk assessment