A Simple Guide To Genomic Testing For Cancer

Genomic testing has transformed cancer care — from diagnosis to treatment selection to prevention. But the landscape of cancer genomic testing can be confusing, with many different types of tests serving different purposes. This guide explains the key types of genomic testing for cancer, what they can tell you, and when each is appropriate.

Two Fundamental Types of Cancer Genetic Testing

Germline Testing (Inherited DNA)

Germline testing analyzes your inherited DNA — the genetic information you were born with and that is present in every cell of your body. It identifies inherited mutations in cancer predisposition genes that increase your lifetime risk of developing certain cancers. Germline testing is done from a blood or saliva sample and is relevant for cancer prevention, risk management, and family counselling.

Key germline cancer genes include BRCA1 and BRCA2 (breast, ovarian, prostate, pancreatic cancer), MLH1, MSH2, MSH6, PMS2 (Lynch syndrome — colorectal, endometrial, ovarian cancer), TP53 (Li-Fraumeni syndrome), PTEN (Cowden syndrome), APC (familial adenomatous polyposis), and CDKN2A (familial melanoma).

Somatic Testing (Tumor DNA)

Somatic testing analyzes the DNA of the tumor itself — the mutations that have accumulated in cancer cells during the development of the cancer. These mutations are not inherited and are not present in normal cells. Somatic testing guides treatment selection by identifying the specific molecular drivers of each patient's cancer.

Key somatic tests include comprehensive genomic profiling (NGS panels covering 300+ cancer genes), specific biomarker tests (EGFR, ALK, ROS1 for lung cancer; HER2 for breast cancer; BRAF for melanoma), and biomarkers predicting immunotherapy response (PD-L1, TMB, MSI).

Liquid Biopsy

Liquid biopsy detects tumor DNA (circulating tumor DNA, or ctDNA) in the blood. It enables non-invasive tumor monitoring without repeated tissue biopsies, early detection of treatment resistance, and — increasingly — early cancer detection in high-risk individuals. Liquid biopsy is particularly valuable for monitoring treatment response and detecting minimal residual disease after treatment.

When Is Each Type of Testing Appropriate?

Germline Testing Is Appropriate When:

• You have a personal or family history of cancer, particularly early-onset or multiple cancers
• You have a cancer type associated with hereditary syndromes (ovarian cancer, male breast cancer, early-onset colorectal cancer)
• You want to understand your inherited cancer risk for prevention and screening purposes
• A family member has been found to carry a cancer predisposition mutation

Somatic Testing Is Appropriate When:

• You have been diagnosed with cancer and treatment decisions need to be made
• Your cancer has progressed on initial treatment and alternative options are being considered
• You are being considered for a clinical trial that requires specific molecular eligibility criteria

FAQs

Do I need genetic counselling before cancer genetic testing?

Genetic counselling is strongly recommended before germline cancer genetic testing. A genetic counsellor helps you understand what the test can and cannot tell you, prepares you for possible results, and helps you navigate the implications for yourself and your family.

Will my insurance cover cancer genetic testing?

Coverage varies by insurer and policy. Germline testing for high-risk individuals (e.g., BRCA testing for those with family history) is increasingly covered. Somatic tumor profiling is often covered as part of cancer treatment. Check with your insurer and discuss with your oncologist.