SUMMARY
Breast cancer is a heterogeneous disease that can be treated by surgery, systemic therapy, and radiotherapy. Adjuvant breast cancer radiotherapy has important implications for patient survival but also causes adverse events. During radiation, not only cancer cells are irradiated, but also normal cells of surrounding tissues. The degree of adverse events after radiotherapy varies among patients with the same treatment scheme, which could be a result of genetic variability. Radiation causes both tumour cell DNA damage and tumour cell death. The double-strand break is the most harmful type of DNA damage following radiation, which can be repaired by homologous recombination. Genetic variability of genes encoding DNA repair proteins can affect their expression and function, which could furthermore impact the degree of successful DNA repair and consequently also radiotherapy outcome.This article describes the association between polymorphisms in genes involved in homologous recombination repair, such as RAD51 rs1801320, rs1801321 and XRCC3 rs861539, rs1799794, and radiotherapy outcome in breast cancer patients.