Tumor DNA Testing vs. Inherited (Germline) Testing

The word "genetic" gets attached to two very different cancer tests. Mixing them up causes confusion.

• Tumor DNA testing (also called biomarker or somatic testing) looks at changes in a person's cancer. It helps guide treatment.
• Inherited (germline) testing looks for changes that have been in every cell since birth. These changes raise cancer risk, and they can be passed to relatives.

Same word, different questions: one is about treating a cancer, the other is about inherited risk.

Biomarker testing is for people who have cancer. It looks for genes, proteins, and other markers in the cancer that can change how treatments work. Each person's cancer has its own pattern of biomarkers.

Key points from the National Cancer Institute:

• The sample is a piece of the cancer. It comes from a biopsy, from surgery, or sometimes from a blood test called a liquid biopsy.
• The changes it finds are mostly acquired (somatic) changes. They arose during life. They cause most cancers, and they cannot be passed to family members.
• Results can guide treatment. Some targeted therapies and immunotherapies only work for cancers with certain biomarkers. Testing can also help find a clinical trial a person may be able to join.

Biomarker testing goes by several names. Tumor testing. Genomic profiling. Molecular profiling. Somatic testing.

Inherited-risk testing asks a different question. Were you born with a change that raises your cancer risk?

• The sample is healthy cells, usually blood or saliva. An inherited change is in every cell, so any cell will do.
• A result can guide screening and prevention. And because the change can be passed down, it carries information for blood relatives.
• People with or without cancer can consider it.

The line is not always sharp. Some biomarker tests compare a tumor with a person's healthy cells. And a tumor test can sometimes turn up a change the person was born with. When that happens, the National Cancer Institute notes that doctors usually recommend a separate germline test. That test confirms whether the change really is inherited. It matters for the person's own future risk, and for their family. If an inherited change is present, a provider may suggest speaking with a genetic counselor.

• Goal: tumor testing guides treatment. Germline testing weighs inherited risk.
• Sample: tumor testing uses cancer cells. Germline testing uses blood or saliva.
• Passed to family? Tumor (somatic) changes usually are not. Inherited (germline) changes can be.
• Who: tumor testing is for people with cancer. Germline testing can be for people with or without cancer.

Cost can shape which testing happens. For biomarker (tumor) testing, the National Cancer Institute notes that the price varies a lot. It depends on the type of test, the cancer, and the insurance plan. Medicare and Medicaid cover some biomarker tests for people with advanced cancer. Private insurers often cover a test when there is enough proof it is needed to guide treatment.

Inherited (germline) testing and counseling are usually covered by health insurance too, when they are considered medically necessary. But coverage varies. Checking with your provider and your insurer first helps you avoid surprises. Some programs offer testing at a reduced cost, or no cost, for people who qualify.

Both tests can be useful. But they are not interchangeable. Work out which question you are trying to answer. How should this cancer be treated? Or is an inherited risk present? The question points to the right test. A doctor or genetic counselor can explain which one fits your situation, and what its results would mean.