Prostate cancer invading rectal serosa and anal sphincter treated with definitive radiation therapy: Case report and review of the literature.

Despite anatomical proximity, prostatic adenocarcinoma with rectal invasion is rare. We describe a case of prostate cancer invading the anal sphincter, treated with radiation therapy (RT). A 78-year-old patient underwent definitive radiotherapy in 2018 because of poorly differentiated adenocarcinoma, Gleason 4 + 3 (7). The initial stage was mrT4N0 on magnetic resonance imaging (MRI) images. The pre-treatment prostate-specific antigen level was 142 ng/mL, and the patient was subjected to androgen deprivation therapy. RT was performed using volumetric modulated arc therapy (VMAT) and a dose of 76 Gy in 38 fractions. After 2 months, MRI showed a complete response. During RT, toxicity was limited to mild gastro-intestinal and urologic symptoms. This report is the first to describe prostate cancer invasion of the anal sphincter and to extend to that condition the use of RT - already regarded as a useful treatment option for inoperable locally advanced high-risk prostate cancer (PC). This study suggests that VMAT can be a safe and effective treatment option for locally advanced high-risk PC patients.