Risk of congenital anomalies in children who have a sibling with cancer: A matched cohort study.

ABSTRACT

PURPOSE: We assessed the risk of congenital anomalies in children who have a sibling with cancer. METHODS: We performed a matched cohort study of children born between 2006 and 2022 in Quebec. The exposure was having a sibling with cancer. Exposed children were matched to unexposed children based on sex, number of siblings, birth order, and year. The outcome included heart defects, orofacial clefts, and other anomalies. Using conditional logistic regression, we estimated odds ratios (OR) and 95 % confidence intervals (CI) for the association between having a sibling with cancer and the likelihood of having a congenital anomaly. RESULTS: A total of 2403 children who had a sibling with cancer were matched to 240,257 unexposed children. Congenital anomalies were more frequent in children who had a sibling with cancer compared with unexposed children (10.3 % vs 8.9 %). Overall, having a sibling with cancer was only weakly associated with congenital anomalies (OR 1.18, 95 % CI 1.04-1.35). Exposed children tended to have greater odds of polydactyly/syndactyly (OR 1.89, 95 % CI 1.11-3.21) and urinary defects (OR 1.50, 95 % CI 1.09-2.08) compared with unexposed children. CONCLUSIONS: Children who have a sibling with cancer have an only weakly elevated risk of congenital anomalies.