Based on the clinical skin reaction of radiotherapy patients we analyzed retrospectively the initial, residual and background DNA damage measured by histone γ-H2AX between the groups of BC patients with normal (RTOG grade 0 and 1, n=31) and an adverse (RTOG grade 3, n=6) skin reaction to RT compared with the healthy donors (Figure 3). This evidence concerns the gene H2AX and breast cancer.