Is childhood cancer hereditary — did we cause this?

Most childhood cancers are not inherited. Roughly 5–10% of cases are linked to an inherited gene change passed down from a parent — the remaining 90–95% arise from random errors that occur during the child's own cell division, or from factors that alter cell DNA during development in the womb or early childhood. This means that in the vast majority of cases, neither parent did anything to cause the cancer. When an inherited genetic factor is involved, it is typically identified through genetic counselling, and the family is guided on monitoring and screening options.

No. This is one of the most painful questions parents carry, and the answer is clear: you did not cause your child's cancer. Childhood cancer is not caused by anything a parent did or did not do during pregnancy or after birth. The overwhelming majority of childhood cancers arise from spontaneous changes in cell DNA that happen before birth or in early childhood — changes that are beyond any parent's control. Feeling guilt and self-blame is a very common and understandable response to a devastating diagnosis, but there is no scientific basis for it. Your energy is better spent on treatment and being present for your child — and our team walks every step of this journey with you.

Every cancer involves mutations — changes in a cell's DNA that cause it to grow without stopping. In childhood cancer, most of these mutations are “somatic” (also called acquired): they arise in a single cell during the child's development and are not present in the parents' genes. A hereditary or “germline” mutation is different — it is present in every cell of the body from birth because it was inherited from a parent's egg or sperm. Germline mutations can predispose a child to certain cancers, but having the mutation does not guarantee cancer will develop. Genetic counselling can identify whether a germline mutation is present and what it means for the family.

A small number of childhood cancers are more strongly associated with inherited predisposition syndromes. For example, children with Down syndrome (trisomy 21) have a higher risk of developing leukemia. Retinoblastoma — a cancer of the eye — has a hereditary form caused by a mutation in the RB1 gene. Li–Fréaumeni syndrome, caused by a TP53 mutation, is associated with several childhood cancers including brain tumours, bone sarcomas, and adrenal cancers. Neurofibromatosis type 1 (NF1) increases the risk of certain nerve-sheath tumours. It is important to note that having these conditions raises risk — it does not make cancer inevitable, and not all children with these syndromes develop cancer.

Whether family members need testing depends on the specific cancer, the child's age at diagnosis, and whether there is a pattern of related cancers in the family. A genetic counsellor — a specialist trained to evaluate cancer family history — will review this with you in detail. As a general guide, genetic evaluation of the family is considered when: the same or related cancers appear in multiple close relatives; a relative developed cancer at an unusually young age (particularly before 50); or the child's cancer type is known to have a hereditary form. At CION, we can refer families to appropriate genetic counselling services and coordinate follow-up care.

In most cases, a sibling's risk is not meaningfully elevated above the general population, because most childhood cancers are not inherited. If a hereditary mutation is identified in the child with cancer, siblings can be tested to see whether they carry the same mutation. If they do, this does not mean they will develop cancer — it means they benefit from closer monitoring and early-detection measures. Decisions about testing siblings, particularly younger children, are guided by the type of mutation and what protective actions are available. A genetic counsellor will help the family understand the specific implications for each family member.