We report a case of a sarcomatous transformation of a prostatic adenocarcinoma after radiotherapy and chemotherapy. The sarcomatous tumor showed features of myogenic differentiation. DNA flow cytometry demonstrated a change in the DNA ploidy, from a diploid pattern in the adenocarcinoma, to an aneuploid pattern in the sarcoma. This is the first report of a prostatic sarcomatous tumor studied in this way. Review of medical literature revealed five additional cases of prostatic adenocarcinoma undergoing sarcomatous transformation following radiotherapy with or without chemotherapy or hormonal therapy.