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Genetics

A small but important proportion of cancers is linked to an inherited genetic change. Knowing about it changes both the choice of treatment and the follow-up of healthy family members. This page covers genetic testing, from BRCA and Lynch to liquid biopsy.

  • BRCA1/2 best known inherited change in breast and ovarian cancer
  • Lynch syndrome raising uterine and bowel cancer risk
  • ctDNA liquid biopsy reading tumour DNA from blood

What is inherited cancer risk?

Not every cancer is inherited. Most arise from random changes that accumulate in cells over a lifetime. In a proportion of cases, however, the person carries a gene change present from birth and passed on by a parent.

Carrying such a change does not mean you will develop cancer; it means your risk is high. Knowing about it means screening can start earlier, risk-reducing options can be discussed, and for some patients the treatment itself changes.

The decision to test is not taken alone. Genetic counselling before and after the test is needed so that the result is understood correctly and family members are guided properly.

Inherited syndromes

These also affect treatment decisions directly, which is why they should be assessed at diagnosis.

  1. BRCA1 / BRCA2

    DNA repair genes

    These genes repair damaged DNA in the cell. An inherited change raises the risk of breast, ovarian, prostate and pancreatic cancer, and also determines eligibility for PARP inhibitor treatment.

  2. Lynch

    The MMR gene family

    Covers MLH1, MSH2, MSH6, PMS2 and EPCAM. It markedly raises the risk of bowel and uterine cancer, and these tumours generally respond well to immunotherapy.

  3. Panel

    Multi-gene panels

    Dozens of cancer predisposition genes can be examined at once from a single blood sample. The panel is chosen according to personal and family history — a wider panel is not always better.

Modern tests

Genetic tests can show not only inherited risk but also the genetic profile of the tumour itself. The two answer different questions.

  1. Germline

    Inherited (germline) test

    Carried out on blood or saliva, it shows changes present in every cell of the body and inherited from a parent. The result concerns not only the patient but siblings and children too.

  2. Somatic

    Tumour genomic profiling

    Carried out on biopsy tissue, it shows changes that have arisen only in the tumour cells. It is used to identify which targeted drug might work.

  3. ctDNA

    Liquid biopsy

    Reads fragments of tumour DNA circulating in the blood. It can be an alternative where a biopsy is not possible and may reveal resistance early. A negative result does not definitively prove the change is absent.

How the testing process works

A genetic test is not simply a blood sample; it is a process with steps before and after.

  1. 01

    Counselling session

    Personal and family cancer history is set out in detail. Which test is appropriate, and what the result could mean, are discussed here.

  2. 02

    Taking the sample

    A single tube of blood is usually enough for an inherited test. Tumour profiling uses existing biopsy tissue, so a new procedure is often unnecessary.

  3. 03

    Interpreting the result

    Results may be positive, negative or a "variant of uncertain significance". That third type is common and does not on its own call for a change in treatment.

  4. 04

    What it means for family

    If an inherited change is found, testing is offered to first-degree relatives. Early screening and risk-reducing options are then planned for those who carry it.

Frequently Asked Questions

Will a genetic test tell me whether I will get cancer?

No. The test shows whether your risk is above average, not whether you will develop cancer. A positive result is not a diagnosis, and a negative result does not mean your risk is zero.

What does "variant of uncertain significance" mean?

It means a change has been found in a gene whose effect is not yet known. This result is not used on its own to decide on treatment or surgery. As scientific knowledge grows, the classification of such variants can change over time.

Does liquid biopsy replace a normal biopsy?

Not entirely, at least not yet. Tissue biopsy remains the gold standard. Liquid biopsy is a valuable complement where a biopsy cannot be taken, or for tracking changes during treatment.

Could my test result affect my insurance or my job?

That depends on the law where you live and on the terms of your policy. Raising it during the pre-test counselling session helps you make an informed decision.

Should my children be tested?

For genes that predispose to adult-onset cancer, testing is generally deferred until adulthood, so that the person can decide for themselves whether to be tested.