Family History of Cancer: — Should You Get Genetic Testing?

Most cancers are not inherited. ASCO estimates that around one in ten cancers across all types are linked to an inherited gene change — the rest arise from a combination of age, lifestyle, and chance.

When a hereditary gene change does run in a family, it raises the absolute lifetime risk of certain cancers. To give you a sense of scale: NCCN notes that the average woman's lifetime risk of breast cancer in the general population is roughly 1 in 8. A woman carrying a BRCA1 or BRCA2 mutation has a substantially higher absolute lifetime risk — NCCN publishes specific ranges by mutation type in its clinical guidelines, and your genetic counsellor will apply these to your family pattern.

Knowing your absolute risk — not just that it is elevated, but by approximately how much — is what shapes the next conversation. A modestly raised risk may mean starting mammograms a few years earlier. A substantially raised risk may mean annual MRI or more frequent colonoscopy. Those are very different decisions, and they begin with knowing your number.

Genetic testing for inherited cancer risk analyses your blood — the DNA you were born with, not tumour tissue. The laboratory looks for inherited changes, called pathogenic variants, in genes known to substantially raise cancer risk.

The most tested genes are BRCA1 and BRCA2, which are linked to elevated lifetime risk of breast and ovarian cancers. Lynch syndrome, caused by changes in genes including MLH1, MSH2, MSH6, and PMS2, raises the lifetime risk of colorectal, uterine, and several other cancers. Depending on your family pattern, a broader multi-gene panel may also examine genes such as PALB2, CHEK2, or ATM.

A positive result does not mean you will develop cancer. It means your risk is high enough to warrant a structured, earlier-start surveillance plan. A negative result — when your family has a confirmed mutation — is genuinely reassuring: your risk returns to the population level. A negative result when no family mutation has been identified means the laboratory did not find a change in the genes it tested; it does not rule out all inherited risk.

If testing confirms you carry a BRCA1 or BRCA2 mutation, NCCN recommends annual breast MRI alongside mammography, generally starting between age 25 and 30. This is earlier than standard population screening because BRCA-related breast cancers can develop during a woman's thirties, and sometimes younger.

For Lynch syndrome mutation carriers, NCCN and ASCO recommend colonoscopy every one to two years, starting at age 20 to 25 — or ten years before the youngest age at which a family member was diagnosed, whichever comes first. Annual surveillance for uterine and ovarian cancer is also recommended for Lynch syndrome carriers.

If no mutation is found but your family history is strongly suggestive, NCCN guidance is to begin surveillance ten years before the youngest affected relative's age at diagnosis. That gives you a concrete starting point while your oncologist continues to assess the full family pattern.

Your exact schedule will be written by a genetic counsellor working from your pedigree — not a general guideline applied to everyone, but a plan matched to your actual level of risk.