Parental age, family size, and offspring's risk of childhood and adult acute leukemia.

BACKGROUND An association between childhood acute leukemia and advanced parental age was observed more than 50 years ago, and the association has been repeated in several, but not all, subsequent studies. In contrast to the many studies addressing childhood leukemia, few have included adult patients. METHODS In this register-based case-control study, we examined the association between parental age and incidence of acute leukemia in 2,660 childhood cases and 4,412 adult cases of acute leukemia, compared with 28,288 age-matched controls selected from a population-based register. Relative risks were estimated with conditional logistic regression. RESULTS We found a small increased risk of childhood acute lymphoblastic leukemia with increasing paternal age (adjusted OR, 1.05 per 5-year increase in age). Risk estimates were similar for childhood acute myeloid leukemia (AML), whereas no association was found with adult leukemia. Meanwhile, we observed a decreased risk of adult AML with increasing number of siblings, both older and younger. CONCLUSIONS The results support the idea of a prenatal etiology of leukemia but indicate that parental age effects are limited to childhood cases. IMPACT This is the first large study on parental age and leukemia risk, which includes adult cases. The finding on family size and risk of adult AML needs to be validated in future studies.