Identification of genetic predispositions related to ionizing radiation in primary human skin fibroblasts from survivors of childhood and second primary cancer as well as cancer-free controls: Protocol for the nested case-control study KiKme. (Preprint)

BACKGROUND Therapy of a first primary neoplasm (FPN) in childhood with high doses of ionizing radiation is an established risk factor for second primary neoplasms (SPN). An association between exposure to low doses and childhood cancer is also suggested, however, results are inconsistent. As only subgroups of children with FPNs develop SPNs, an interaction between radiation, genetic, and other risk factors is presumed to influence cancer development. OBJECTIVE Therefore, the population-based nested case-control study KiKme aims to identify differences in genetic predispositions and radiation-response between childhood cancer survivors with and without SPNs as well as cancer-free controls. METHODS We conducted a population-based nested case-control study KiKme. Besides questionnaire information, skin biopsies and saliva samples are available. By measuring individual reactions to different exposures of radiation (e.g., 0.05 and 2 Gray) in normal somatic cells of the same person, our design enables us to create several exposure scenarios for the same person simultaneously and measure several different molecular markers (e.g., deoxyribonucleic acid (DNA), messenger RNA, long non-coding RNA, copy number variation). RESULTS Since 2013, 101 out of 247 invited SPN patients, 340 out of 1,729 invited FPN patients, and 150 out of 246 invited cancer-free controls were recruited and matched by age and sex. Childhood cancer patients were additionally matched by tumor morphology, year of, and age at diagnosis. Participants reported on lifestyle, socio-economical and anthropometric factors, as well as on medical radiation history, health, and family history of diseases (N = 556). Primary human fibroblasts from skin biopsies of the participants were cultivated (N = 499) and cryopreserved (N = 3,886). DNA was extracted from fibroblasts (N = 488) and saliva (N = 510). CONCLUSIONS This molecular-epidemiological study is the first to combine observational epidemiological research with standardized experimental components in primary human skin fibroblasts to identify genetic predispositions related to ionizing radiation in childhood and SPNs. In the future, fibroblasts of the participants will be used for standardized irradiation experiments, which will inform analysis of the case-control study and vice versa. Differences between participants will be identified using several molecular markers. With its innovative combination of experimental and observational components, this new study will provide valuable data to forward research on radiation-related risk factors in childhood cancer and SPNs.