The aim was to study the relationship between cellular radiosensitivity or double-strand break (dsb) repair capacity of skin fibroblasts and the extent of acute reaction after radiotherapy for breast cancer. The study was performed with 25 breast cancer patients submitted to the radiotherapy unit of the Egyptian National Cancer Institute after conserving surgery. Dermal fibroblasts, established from skin biopsies, were used to determine the cellular radiosensitivity via colony assay and the capacity of dsb repair by constant-field gel electrophoresis. Acute reactions were scored using the Radiation Therapy Oncology Group (RTOG) classification. The spectrum of acute reactions varied from grade 1 to 4, whereby most patients developed a grade 1 reaction after total doses ranging between 46 and 70 Gy. Skin fibroblasts showed a pronounced variation in both cellular radiosensitivity expressed as the mean inactivation dose (Dbar) (coefficient of variation, CV=25%) as well as in the number of residual dsb (CV=33%) with no significant correlation between these two endpoints (r2=0.20, p=0.14). Both parameters did not correlate with the extent of acute reaction of the respective patient. The data obtained indicate that the sensitivity of fibroblasts measured either by colony assay or by dsb repair capacity is not a major parameter determining the extent of acute reaction after radiotherapy of breast cancer patients.
