Genetic testing & counselling for childhood cancer families

Genetic testing for childhood cancer looks for inherited (germline) mutations — changes in DNA that were present from birth and may have contributed to the cancer developing. Not every child with cancer needs germline testing. It is typically recommended when the child’s cancer type has a known hereditary form, when the child’s age at diagnosis is unusually young for that cancer type, or when there is a pattern of related cancers in close family members. Your child’s oncologist will tell you whether germline testing is clinically appropriate for your situation. At CION, every child’s case is reviewed by a multi-specialist tumor board, which includes the expertise to identify when genetic evaluation adds useful information to the care plan.

Germline testing looks at DNA from a blood or saliva sample taken from the child — not from the tumour itself. It identifies mutations that are present in every cell of the body from birth, meaning they were inherited from a parent. Tumour testing (also called somatic or molecular testing) analyses DNA from the tumour tissue and looks for mutations that arose only in the cancer cells. A child can have somatic tumour mutations without having any inherited germline mutation — this is the case in the majority of childhood cancers. Germline testing answers the question: ‘Did my child inherit a predisposition to cancer?’ Tumour testing answers: ‘What is driving this specific cancer?’ Both are useful — but for different questions.

Family genetic counselling for cancer is a structured conversation — usually with a specialist called a genetic counsellor — that reviews your family’s cancer history, explains what genetic testing can and cannot tell you, helps you decide whether testing is right for your family, and interprets the results if testing is done. The first session typically takes 60 to 90 minutes and does not require any testing commitment. The counsellor will map out which relatives on both sides have had cancer, at what ages, and look for patterns that suggest a hereditary predisposition. The outcome is a clear, personalised explanation of your family’s risk picture, a recommendation on whether testing is warranted, and — if a mutation is found — a plan for monitoring family members who may also carry it.

A small but important subset of childhood cancers is associated with known genetic predisposition syndromes. Retinoblastoma — a cancer of the retina — has a well-established hereditary form caused by mutations in the RB1 gene, especially when it affects both eyes. Li–Fréaumeni syndrome (TP53 mutations) is linked to several childhood cancers including brain tumours, bone sarcomas, and adrenocortical carcinoma. DICER1 syndrome is associated with rare lung, kidney, and thyroid tumours in children. Beckwith–Wiedemann syndrome raises risk for Wilms tumour (kidney cancer) and hepatoblastoma. Children with Down syndrome have an elevated risk of certain leukemias. These are well-studied examples, not an exhaustive list. A genetic counsellor can assess whether your child’s specific cancer type and family history warrant further evaluation.

Finding a germline mutation in your child means that one or both parents likely carry the same mutation, because germline mutations are inherited — they come from egg or sperm. However, not everyone who carries the mutation will develop cancer. The next step after a positive finding in the child is “cascade testing” — offering the same genetic test to parents and, based on those results, to siblings and other close relatives. Each family member’s result is their own private information, and testing is always a personal decision. A genetic counsellor will explain what the specific mutation means for each relative: the level of cancer risk it carries, whether there are effective screening strategies, and whether any preventive steps are available. The goal is to turn uncertainty into actionable information.

Genetic testing can tell you whether an inherited predisposition mutation is present — but it cannot always explain exactly why cancer developed in your child. Even when a predisposition mutation is found, carrying that mutation is only one factor; most people who carry such mutations do not develop cancer. In the majority of childhood cancer cases, no germline mutation is found, which does not mean the test failed — it means your child’s cancer is most likely not hereditary, and siblings and parents carry no elevated inherited risk. If testing does not find a mutation, the cancer’s cause remains the same as for most childhood cancers: spontaneous DNA errors during early development, which are not passed on and are not anyone’s fault.