To investigate the possible role of circulating levels of cytokines IL-6 and TGF-β1 in the occurrence and severity of adverse effects of radiotherapy for prostate cancer, we examined the possible relationships between serum concentrations of IL-6 and TGF-β1 determined before radiotherapy and after the 25th radiotherapy fraction, and acute GU and GI radiotoxicity, as well as fatigue. This evidence concerns the gene IL6 and prostate cancer.