Infant birthweight and risk of childhood cancer: international population-based case control studies of 40 000 cases

Background: High birthweight is an established risk factor for childhood leukaemia. Its association with other childhood cancers is less clear, with studies hampered by low case numbers. Methods: We used two large independent datasets to explore risk associations between birthweight and all subtypes of childhood cancer. Data for 16 554 cases and 53 716 controls were obtained by linkage of birth to cancer registration records across five US states, and 23 772 cases and 33 206 controls were obtained from the UK National Registry of Childhood Tumours. US, but not UK, data were adjusted for gestational age, birth order, plurality, and maternal age and race/ethnicity. Results: Risk associations were found between birthweight and several childhood cancers, with strikingly similar results between datasets. Total cancer risk increased linearly with each 0.5kg increase in birthweight in both the US [odds ratio 1.06 (95% confidence interval 1.04, 1.08)] and UK [1.06 (1.05, 1.08)] datasets. Risk was strongest for leukaemia [USA: 1.10 (1.06, 1.13), UK: 1.07 (1.04, 1.10)], tumours of the central nervous system [USA: 1.05 (1.01, 1.08), UK: 1.07 (1.04, 1.10)], renal tumours [USA: 1.17 (1.10, 1.24), UK: 1.12 (1.06, 1.19)] and soft tissue sarcomas [USA: 1.12 (1.05, 1.20), UK: 1.07 (1.00, 1.13)]. In contrast, increasing birthweight decreased the risk of hepatic tumours [USA: 0.77 (0.69,