The aim of this work was to investigate the possibility of prediction of early skin reactions in breast cancer patients treated with postoperative conservative breast therapy through studying the relationship between DNA double strand break (DSB), cell killing and early skin reactions. Skin biopsy was obtained from 40 breast cancer patients, clonogenic assay was applied for 20 patients only and residual DNA double strand break (DSB) was measured in 17 patients. No correlation was found between early skin reaction and SF2 as well as with residual DNA DSBs. The study showed a positive relationship between breast size and acute skin reactions of the patients.