Determination of Predictive Genetic Markers of Toxicity After Hypofractionated Radiotherapy in Breast Cancer Patients Post-Conservative Surgery

The single shot partial breast irradiation (SSPBI) trial was designed as a prospective Phase II "single-arm study". The use of a single dose tumor bed is expected to be very effective in terms of tumor control, but it could increase the incidence of radiation induced erythema. Therefore, the investigators assumed that a decreased DNA repair capability, as well as a reduced detoxification of the damage caused by oxidative stress could explain the increased acute toxicity, i.e. a higher incidence of erythema after a single dose. For this reason the investigators decided to investigate SNPs of genes involved in antioxidant and DNA damage repair pathways such as GST, XRCC1, XRCC3 and RAD51.

The investigators assumed an erythema rate of 20% and 54% in patient groups at low and high risk, respectively, (groups were identified based on the absence/presence of the above polymorphisms alone or in combination), thus the minimum sample size was 56 patients with α=0.05, 2-tailed test and a power of the study of 80%.