Secondhand Smoke Exposure during Childhood and Cancer Mortality in Adulthood among Never Smokers: the Japan Collaborative Cohort Study for Evaluation of Cancer Risk

We examined whether secondhand smoke exposure during childhood was associated with cancer mortality in adulthood among never smokers. In the Japan Collaborative Cohort Study, we analyzed data from 45,722 Japanese lifetime non-smokers who were aged 40–79 years with no history of cancer at the baseline (1988–1990) and completed a lifestyle questionnaire including the number of family members who smoked at home during their childhood (0/1/2/3+ members). The Cox proportional hazards model and competing risk regression were used to calculate the multivariable hazard ratios (HRs) and subdistribution hazard ratios (SHRs) with 95% confidence intervals (CIs) of all and site-specific cancer mortality, according to the number of smoking family members during the participant’s childhood after adjusting for potential confounding factors. During the median follow-up of 19.2 years, a total of 2,356 deaths from cancer were documented. Secondhand smoke exposure was positively associated with the risk of mortality from pancreatic cancer in adulthood; the multivariable HR of 3+ smoking family members was 2.32 (95% CI: 1.14, 4.72), compared with 0 members. The associations were not evident for the risks of total or other types of smoking-related cancers. In conclusion, secondhand smoke exposure during childhood was associated with an increased risk of mortality from pancreatic cancer in adulthood.