Selection of subjects

Tissue harvest and experiments were performed prospectively in accordance and with the approval of the ethical committee of the Ruhr University Bochum (Clinical Trial approval number: 16-5932-BR). Female patient were included in the study who suffered malignant breast cancer over the last 3 years followed by radiation. Informed consent was obtained from female patients between the ages of 30 and 55 without any acute or chronic muscular disease, infection, malignant (except malignant breast cancer) or autoimmune disease. After acquisition of informed consent, a muscle biopsy (size ~0.5 cm³) was collected during a microsurgical breast reconstruction from the radiated pectoralis muscle, and an intraindividual control from the rectus abdominis muscle, while preparing these tissues for the microsurgical procedure. Tissue biopsies were directly either frozen to −80 °C or fixed in paraformaldehyde.