Background: Research on germline genetic variants relies on enough eligible participants which is difficult to achieve for rare diseases such as childhood cancer. With self-collection kits, participants can contribute genetic samples conveniently from their home. Demographic and clinical factors were identified previously that influenced participation in mailed self-collection. People with pre-existing heritable diagnoses might participate differently in germline DNA collection which might render sampling biased in this group. In this nationwide cross-sectional study, we analysed predictive factors of participation in DNA self-collection including heritable diagnoses.

Methods: We identified childhood cancer survivors from the Swiss Childhood Cancer Registry for invitation to germline DNA self-sampling in September 2019. Participants received saliva sampling kits by postal mail at their home, were asked to fill them, sign an informed consent, and send them back by mail. Two reminders were sent to non-participants by mail. We compared demographic, clinical, and treatment information of participants with non-participants using univariable and multivariable logistic regression models.

Results: We invited 928 childhood cancer survivors in Switzerland with a median age of 26.5 years (interquartile range 19-37), of which 463 (50%) participated. After the initial send out of the sampling kit, 291 (63%) had participated, while reminder letters led to 172 additional participants (37%). Foreign nationality (odds ratio [OR] 0.5; 95%-confidence interval [CI] 0.4-0.7), survivors aged 30-39 years at study versus other age groups (OR 0.5; CI 0.4-0.8), and survivors with a known cancer predisposition syndrome (OR 0.5; CI 0.3-1.0) were less likely to participate in germline DNA collection. Survivors with a second primary neoplasm (OR 1.9; CI 1.0-3.8) or those living in a French or Italian speaking region (OR 1.3; CI 1.0-1.8) tended to participate more.

Conclusions: We showed that half of childhood cancer survivors participated in germline DNA self-sampling relying completely on mailing of sample kits. Written reminders increased the response by about one third. More targeted recruitment strategies may be advocated for people of foreign nationality, aged 30-39 years, and those with cancer predisposition syndromes. Perceptions of genetic research and potential barriers to participation of survivors need to be better understood.