Alterations in pectoralis muscle cell characteristics after radiation of the human breast in situ.

The life-time risk of being diagnosed with breast cancer is ~12%, hence breast cancer is by far the most common cancer among women. The multimodal treatment concept of breast cancer often intends radiation. The utilized ionizing radiation leads changes in the tissue resulting in tissue damage due to an alteration of molecular factors. The goal of this study was to identify the role of muscle-catabolic proteins after radiation of human pectoralis major muscles in situ. Tissue of the pectoralis major muscle was collected in 12 breast cancer patients after radiation (maximum 3 years after radiation) undergoing a deep inferior epigastric perforator free-flap breast reconstruction. At the same time, an intraindividual comparison to rectus abdominis muscle was carried out upon free-flap elevation. Immunological properties, cell proliferation, differentiation as well as the expression profile of the muscle tissue were investigated through immunohistological reactions, a DNA-microarray and histology. We found significantly increased neutrophil immigration in the radiated muscle tissue. At the same time, proteins responsible for muscular atrophy and apoptosis were significantly elevated in immunohistochemistry. A DNA microarray detected immunological upregulation and myo-differentiative disorders in radiated muscle tissue. This novel study investigating catabolism in radiated muscle in situ can serve as a basis for the treatment of radiation-accompanied muscle disorders.