Background: Passive exposure to cigarette smoke has negative effects on respiratory health. Childhood cancer survivors (CCS) are at increased risk for respiratory disease due to treatment regimens that may harm the respiratory system. The objective of this study was to assess the prevalence of parental smoking among CCS and investigate its association with respiratory outcomes.

Procedure: As part of the Swiss Childhood Cancer Survivor Study, between 2007 and 2022, we sent questionnaires to parents of children aged ≤16 years who had survived ≥5 years after a cancer diagnosis. Parents reported on their children's respiratory outcomes including recurrent upper respiratory tract infections (otitis media and sinusitis), asthma, and lower respiratory symptoms (chronic cough persisting >3 months, current and exercise wheeze), and on parental smoking. We used multivariable logistic regression to investigate associations between parental smoking and respiratory outcomes.

Results: Our study included 1037 CCS (response rate 66%). Median age at study was 12 years (interquartile range 10-14 years). Eighteen percent of mothers and 23% of fathers reported current smoking. CCS exposed to smoking mothers were more likely to have recurrent upper respiratory tract infections (OR 2.1; 95%CI 1.1-3.7) and lower respiratory symptoms (OR 2.0; 95%CI 1.1-3.7). We found no association with paternal smoking.

Conclusions: A substantial proportion of CCS in Switzerland have parents who smoke. Exposure to maternal smoking was associated with higher prevalence of upper and lower respiratory problems. Healthcare providers can support families by addressing caregiver smoking behaviors and providing referrals to smoking cessation programs.