How Genes Factor Into Cancer Risk

Cancer develops when cells acquire changes — called mutations — that allow them to grow and divide without the normal controls. Most of those mutations accumulate gradually over a lifetime due to aging, environmental exposures, or random errors in cell copying. But in some families, a mutation is already present at birth, inherited from a parent. These are called germline variants, and they can lower the threshold at which cancer develops.

It is important to keep perspective: inherited variants are estimated to account for roughly 5–10% of all cancers. The large majority of cases arise from non-inherited causes, which is why age, lifestyle, and environment remain central to any discussion of overall cancer risk factors.

Germline variant

A gene change that is present in every cell of the body from birth because it was inherited from a parent. Unlike mutations that develop over a lifetime, germline variants can be passed to children.

Hereditary cancer syndrome

A pattern of cancer risk caused by an inherited gene variant that significantly increases the likelihood of developing specific cancer types, often at a younger-than-typical age.

Genetic counselling

A conversation with a trained specialist who helps individuals understand what genetic testing involves, what results mean, and how they might affect personal and family health decisions.

BRCA1 / BRCA2

Two genes whose normal function is to suppress tumour growth. Inherited variants in either gene are associated with a notably higher lifetime risk of breast and ovarian cancer, among others.

Lynch syndrome

One of the most common hereditary cancer syndromes, caused by inherited variants in DNA-repair genes. It significantly raises the risk of colorectal cancer and certain other cancers.

Still, for the individuals and families who carry these variants, understanding the hereditary component can meaningfully shape how they approach screening and prevention. The key is accurate information rather than alarm.

Not all cancers carry the same degree of hereditary influence. Research has identified several cancer types where inherited gene variants play a particularly well-established role:

  • Breast and ovarian cancer: Variants in the BRCA1 and BRCA2 genes are among the most studied inherited cancer risks. See our plain-language BRCA explainer for what these variants mean in practice. For older women, understanding these risks connects directly to breast cancer risk after 60.
  • Colorectal cancer: Lynch syndrome — caused by variants in a group of genes responsible for repairing DNA — significantly raises the risk of colorectal cancer and certain other cancers. It is one of the more common hereditary cancer syndromes.
  • Prostate cancer: A family history of prostate cancer, particularly in a father or brother, is a recognised risk factor. Some prostate cancers also involve BRCA2 variants.
  • Kidney cancer: Certain inherited syndromes, such as Von Hippel-Lindau disease, are linked to higher kidney cancer risk. Our kidney cancer overview covers this in more detail.

Having one of these risk factors does not guarantee illness. It means a more tailored, informed conversation with a healthcare provider is warranted.

Patterns Matter More Than One Case

A single relative with cancer is not necessarily a sign of hereditary risk — cancer is common, and most cases are not inherited. What warrants closer attention is a pattern: multiple relatives with the same cancer, diagnoses at unusually young ages, or rare cancer types appearing more than once in a family.

Reading Your Family History as a Health Signal

Your family's cancer history is among the most accessible pieces of genetic information you have. Certain patterns in that history may suggest a hereditary component worth discussing with a doctor:

  • The same cancer type appearing in multiple close relatives (parents, siblings, grandparents)
  • Cancer diagnosed at an unusually young age — for instance, colorectal cancer before age 50
  • Rare cancers or combinations of cancers that are not commonly seen together
  • Cancer in the sex less typically affected, such as breast cancer in a man

Gathering this information does not require specialist knowledge. Writing down what you know — including the type of cancer, the person's relationship to you, and their approximate age at diagnosis — gives a clinician or genetic counsellor meaningful context to work with.

For a fuller picture of what family history can and cannot tell you, see genetic risk and cancer prevention. And to address some common misconceptions that often arise in these conversations, inherited disease risk myths is worth reading alongside this guide.

Genetic Testing and Counselling: What to Expect

Genetic counselling is a conversation — usually with a specially trained health professional — that helps you understand what genetic testing could tell you, what it cannot, and how results might affect your medical care or that of your family members. It typically happens before any testing takes place.

Testing itself usually involves a saliva sample or blood draw. Results can indicate whether you carry a known variant associated with elevated cancer risk. Importantly, a negative result does not eliminate all cancer risk — it reduces the probability that a hereditary cause is involved, but non-hereditary cancers remain possible.

Results Are Not a Diagnosis

A positive result from genetic testing means you carry a variant associated with elevated risk — not that cancer is present or inevitable. Conversely, a negative result does not mean zero risk. Genetic test results are one input among many that a healthcare provider considers when personalising your care.

For older adults who have already had a cancer diagnosis, genetic testing can still provide relevant information — for example, helping adult children understand their own risk. If you are exploring this path, understanding hereditary cancer syndromes offers useful background. Always consult a qualified healthcare provider before making any decisions about genetic testing.

How Hereditary Risk Affects Screening Decisions

For most adults, cancer screening follows population-level guidelines based on age and general health. For those with a significant hereditary risk, guidelines may differ — screenings can start earlier, occur more frequently, or include additional tests not typically recommended at a standard risk level.

For example, people with Lynch syndrome may be advised to begin colonoscopy screening earlier and repeat it more frequently than the general population. Those with BRCA variants may be offered additional imaging options beyond standard mammography.

These decisions are highly individual and should be made with a healthcare provider who knows your full medical and family history. A good starting point for understanding what screenings are generally recommended is our cancer screenings overview for adults over 50. It is also worth recognising that hereditary risk is just one of several cancer risk factors — modifiable vs. non-modifiable risk factors explains how genetic and lifestyle factors interact.

This article is for general informational purposes only and does not constitute medical advice. Please consult a qualified healthcare professional for guidance specific to your health history and circumstances.