Background Passive exposure to cigarette smoke has negative effects on respiratory health. Childhood cancer survivors (CCS) are at an 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 who were under the age of 16 years and who had survived more than 5 years after cancer diagnosis. Parents reported on respiratory outcomes in their children including recurrent upper respiratory tract infections (otitis media and sinusitis), asthma, and lower respiratory symptoms (chronic cough persisting for more than 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 [IQR] 10-14). 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. Physicians should advise and assist families of CCS in their endeavors to quit smoking.

The authors have declared no competing interest.

This study was supported by the Swiss Cancer Research and Swiss Cancer League (Grant no. KFS-5027-02-2020, KFS-5302-02-2021, KLS/KFS-4825-01-2019, KLS/KFS- 5711-01-2022), Childhood Cancer Switzerland, Kinderkrebshilfe Schweiz, Stiftung fuer krebskranke Kinder - Regio Basiliensis, and the University of Basel Research Fund for Excellent Junior Researchers.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The Ethics Committee of the Canton of Bern granted ethical approval to the Swiss Childhood Cancer Registry and the Swiss Childhood Cancer Survivor Study (166/2014; 2021-0146).

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All data produced in the present study are available upon reasonable request to the authors