genes associated with high to intermediate breast cancer risks, like BRCA1/2, ATM, CHEK2, PALB2, are all involved in the DNA damage response pathway. Mutations in these genes may therefore not only contribute to genomic instability and cancer but also to a radiosensitive phenotype, increasing the carcinogenic risk of mammography screening in mutation carriers. The aim of this project is (i) to elucidate if women harbouring a germline mutation in these major breast cancer genes are characterised by an enhanced in vitro chromosomal radiosensitivity and (ii) to gain insight in the molecular pathways (aberrant expression of genes and their regulators: miRNAs and lncRNAs) involved in radiosensitivity and breast cancer predisposition. The development of biomarkers to assess individual radiosensitivity will assist physicians formulating surveillance programs for women with a genetic predisposition for breast