Association between number of siblings and nervous system tumors suggests an infectious etiology

Objective: To estimate the effect of the number of siblings on the risk of histopathologic subtypes of tumors of the nervous system using large population-based data. Methods: The Swedish Family-Cancer Database comprises 13,613 diagnoses of nervous system tumors with histopathologic information. We analyzed the data using Poisson regression models taking into account potential confounding effects of age, birth cohort, socioeconomic status, and family history of cancer. Results: The rate ratios (RR) for having four or more siblings vs none were significantly increased for hemangioblastoma (RR = 1.68), childhood neuroblastoma (RR = 2.01), and ependymoma (RR = 1.83, p trend < 0.01). For age at diagnosis <= 15 years, the RRs for individuals with three or more younger siblings compared to none were 1.34 for astrocytoma, 2.30 for medulloblastoma, 2.61 for ependymoma, 3.71 for meningioma, and 2.13 for neuroblastoma, with significant trends in risk. Non-significant decreased risks were found between the number of older siblings and nervous system tumors. Conclusions: We provide the first reliable quantification of the effects of number of siblings on the risk of nervous system tumors. Sibship size and number of younger siblings correlate with the incidence of childhood nervous system tumors, suggesting a role of infectious agents in the etiology of the disease.