Cancer genetics and hereditary risk
Some cancer risk is inherited. Establishing whether that applies in a given family has implications that extend beyond the person diagnosed — which is why germline testing is discussed differently from tumour testing.
Testing the tumour
Examines alterations that arose in the tumour during a person’s lifetime. These are not inherited and are not passed on. The purpose is to understand this tumour’s biology and identify potential treatment implications.
Testing the person
Examines DNA present in every cell from birth. A germline finding may be shared with relatives and may carry implications for their risk, their screening, and their own testing decisions.
Genetic counselling — family history discussion
A pedigree chart being drawn or discussed. Hands and paper; no identifiable faces or real family data.
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Hereditary cancer
Most cancer is not inherited. A minority arises in people carrying a germline alteration that raises their lifetime risk. Recognised patterns include hereditary breast and ovarian cancer associated with BRCA1 and BRCA2, Lynch syndrome affecting mismatch repair genes, and Li-Fraumeni syndrome associated with TP53 — among others.
Family history
A structured family history remains one of the most informative and least expensive investigations available. Features that raise the question of a hereditary contribution include cancer at unusually young ages, multiple primary cancers in one person, the same or related cancers across generations, and rare cancers that are themselves associated with syndromes.
Variant interpretation
A germline test result falls into one of several classifications, from benign through variants of uncertain significance to pathogenic. Uncertain findings are common, and they are genuinely uncertain — acting on them as though they were pathogenic is a recognised harm.
Classifications are also revised as evidence accumulates. A variant reported some years ago may since have been reclassified in either direction, which is one reason older reports are worth revisiting.
Cascade testing
Where a pathogenic germline variant is identified, relatives can be tested for that specific variant. Those who do not carry it can generally be reassured; those who do can consider surveillance or prevention options.
Cascade testing is one of the clearest instances in medicine where a single result benefits several people. It also raises questions about how, and by whom, relatives are informed.
Risk communication and genetic counselling
Risk figures are easy to state and hard to convey. A lifetime risk is not an annual risk; a relative risk is not an absolute one; and population figures are not individual predictions.
Accredited genetic counselling services exist for this reason. Where formal counselling is indicated, the appropriate step is a referral to such a service — not a substitute for it.
Prevention and surveillance
Where increased risk is established, options typically fall into surveillance — earlier or more frequent screening — and risk-reducing interventions. These are significant decisions with real trade-offs, taken over time and with the treating and genetics teams rather than at a single appointment.