Genetic Testing: Germline and Somatic

Germline testing provides a foundational understanding of a patient’s cancer risk and potential familial implications, while somatic testing targets the here and now, offering insights that tailor treatment to the cancer’s present genetic state. 

When it comes to guiding care for men with metastatic prostate cancer, two complementary forms of genetic testing, germline and somatic, play crucial roles. Together they offer a comprehensive view of both inherited risks and the unique genetic landscape of the cancer itself, enabling precision medicine to truly shine. Germline testing focuses on inherited mutations, examining DNA from non-cancerous cells such as those found in blood or saliva. These genetic alterations are present in every cell of the body and can reveal hereditary risks that extend beyond the patient. In approximately 10 to 12 percent of men with metastatic prostate cancer, germline testing uncovers clinically actionable mutations such as those in BRCA1, BRCA2, or other homologous recombination repair genes. These findings can open doors to targeted therapies like PARP inhibitors, while also alerting family members to their potential cancer risks.

Somatic testing, in contrast, zeroes in on the tumor itself. By analyzing DNA from cancer cells, either through a direct tumor biopsy or circulating tumor DNA in the blood, this approach identifies mutations acquired as the cancer evolves. These mutations are often distinct from the patient’s inherited genetic profile and are detected in about 20-25% of metastatic prostate cancer cases. Somatic testing can guide the immediate selection of personalized treatments, such as immunotherapies or targeted therapies, based on the tumor’s current genetic makeup.
The distinction between these two tests lies in their focus and timing. Germline testing examines normal cells and addresses lifelong inherited risk, while somatic testing analyzes tumor cells to identify actionable mutation for current treatment strategies. Germline tests are normally performed once, as the inherited genetic profile remains constant, but somatic tests may need to be repeated if the cancer progresses or recurs, reflecting the tumor’s ongoing genetic evolution.
Together, these tests form a powerful diagnostic duo. Germline testing provides a foundational understanding of a cancer’s risk and potential familial implications, while somatic testing targe the here and now, offering insights that tailor treatment to the cancer’s present genetic state. By integrating both, doctors can craft a treatment plan that’s not only precise and effective, but also forward-thinking, considering the patient’s broader health context and family history.