Genetic Testing After a Cancer Diagnosis

After a cancer diagnosis you may be offered genetic testing twice, for two different reasons.

Somatic testing — also called tumor testing or biomarker testing — reads the DNA inside the cancer itself. It asks what is driving this particular tumor and whether a targeted drug exists for it. Those changes arose during your lifetime, in that tissue. They are not in the rest of your body and they cannot be passed to your children.

Germline testing reads the DNA you were born with, usually from blood or saliva. It asks whether you inherited a change that raised your risk in the first place, and therefore whether your blood relatives may carry it too.

This is the distinction people most often miss. A tumor report that mentions BRCA does not tell you whether that change is inherited. Only germline testing answers that, and the National Cancer Institute is explicit that tumor testing does not replace testing for inherited cancer risk. If a tumor test flags something that might be germline, your team may order a separate blood test to confirm it.

National guidelines recommend germline testing for everyone diagnosed with ovarian cancer, pancreatic cancer, male breast cancer, or metastatic prostate cancer. It is also recommended for many people with triple-negative breast cancer, or colorectal cancer diagnosed before age 50. Testing is considered when cancer appears young, when one person has had more than one primary cancer, when several relatives on the same side of the family are affected, or when a relative already carries a known variant.

In practice, testing is offered far less often than guidelines suggest. An analysis of more than a million people with cancer reported by NCI found only about 7% had germline testing — including 38% of those with ovarian cancer and 5.6% of those with pancreatic cancer. If no one has raised it and you fit one of these groups, it is reasonable to ask directly.

A germline result can affect your own care in three ways.

• Treatment. Some inherited variants open specific options, such as PARP inhibitors in BRCA-related ovarian, breast, pancreatic and prostate cancers.
• Surgery and surveillance. Knowing you carry a variant may change the scope of surgery you choose, or add screening at a different site.
• Long-term follow-up. Certain syndromes carry raised risk of a second, unrelated cancer, which changes what your team watches for in the years ahead.

It also changes things for people who are not in the room. Most cancer predisposition variants follow autosomal dominant inheritance: each child, sibling and parent has a 50% chance of carrying the same variant. Your result is what lets them be tested for that one specific change — called cascade testing — which is faster and clearer than starting from scratch.

The Genetic Information Nondiscrimination Act (GINA, 2008) makes it illegal for health insurers to use genetic information for eligibility, coverage or premiums, and for employers with 15 or more employees to use it in hiring, firing, pay or promotion.

GINA does not cover life insurance, disability insurance or long-term care insurance. In most states those insurers may still ask about genetic test results and act on them. GINA also does not restrict the US military in employment decisions, and does not apply to employers with fewer than 15 staff. Some states have passed broader laws.

This gap is rarely mentioned in clinic. It is worth knowing before you test, particularly if you were planning to buy or increase any of those policies.

Testing normally runs through genetic counseling, before and after. The pre-test conversation covers a three-generation family history, which genes the panel includes, what each possible result would and would not tell you, cost and coverage, and written informed consent. Results typically take a few weeks.

Ask for a copy of the full report rather than a summary sentence. Relatives and future clinicians will need the exact gene and variant name, and reports are easier to obtain now than years later.

• NCI — Few People with Cancer Undergo Germline Testing
• NCI — Biomarker Testing for Cancer Treatment
• National Human Genome Research Institute — Genetic Discrimination and GINA