Birth characteristics and risk of prostate cancer: the contribution of genetic factors.

BACKGROUND Prostate cancer has a strong hereditary component, but it has been proposed that hormonal influences in utero may contribute to offspring risk. We investigated the associations between birth characteristics and the risk of prostate cancer in twins, and whether possible associations could be confounded by familial factors, such as shared environment and common genes. METHODS All like-sexed male twins in the Swedish Twin Registry, born from 1926 to 1958 and alive in 1973, were eligible. Data were obtained from birth records, and 11,420 male twins with reliable birth weight data were included in the final study population. Hazard ratios with 95% confidence intervals (CI) from Cox regression models were used to estimate associations between birth characteristics and risk of prostate cancer. Paired analysis was done to account for potential confounding by familial factors. RESULTS Compared with twins with a birth weight of 2,500 to 2,999 g, the hazard ratio (95% CI) for twins with a higher birth weight (>or=3,000 g) corresponded to 1.22 (0.94-1.57). In analyses within twin pairs, in which both twins had a birth weight of >or=2,500 g, a 500 g increase in birth weight was associated with an increased risk of prostate cancer within dizygotic twin pairs (odds ratio, 1.41; 95% CI, 1.02-1.57), but not within monozygotic twin pairs (odds ratio, 1.06; 95% CI, 0.61-1.84). CONCLUSIONS High birth weight is associated with an increased risk of prostate cancer. The difference in risk within dizygotic and monozygotic twin pairs may be due to genetic factors playing an important role in this association.