Smoking and testicular cancer: A Danish nationwide cohort study

Testicular cancer (TC) incidence has increased worldwide, but specific exposures of TC still need investigation. In this cohort study, we investigated the association between mothers' smoking and the risk of TC in their sons. TC was divided into the morphological subtype seminoma and non-seminomas. Because information about maternal smoking was not available in the study period maternal lung cancer diagnosis was used as a proxy for maternal smoking, making it possible for 51 years of complete follow-up. We used the nationwide Danish Cancer Registry and the Danish Civil Registration System to identify all mother-son pairs born from 1968 to 2005 (n = 1329,225). In 20,533 mother-son pairs, the mother was diagnosed with lung cancer, with 140 TC cases. 4136 TC cases were identified for 1308,693 mother-son pairs without lung cancer. Kaplan-Meier survival curves were used to show descriptive statistics for both morphological subtypes. We used Cox proportional hazards regression analysis to estimate the hazard ratio (HR) and 95 % CI for the association between a mother's lung cancer diagnosis and the risk of getting TC. Men born by a mother developing lung cancer had an increased hazard of getting testicular cancer (HR=1.28, 95 % CI 1.08-1.51) when adjusting for maternal age at birth and maternal birth year. The results differ for seminomas (HR=1.52, 95 % CI 1.23-1.88) and non-seminomas (HR=0.97, 95 % CI 0.72-1.29). These findings, based on the long follow-up and nationwide data, suggest an increased risk of testicular cancer for seminomas in the sons of mothers with a lung cancer diagnosis, suggesting that smoking during pregnancy or in childhood could be associated with the son being diagnosed with testicular seminoma.