Anal Canal Squamous Cell Carcinoma Following Low-Dose-Rate Prostate Brachytherapy: A Report of Two Cases and Literature Review.

We report two cases of anal canal squamous cell carcinoma (SCC) that developed following low-dose-rate (LDR) brachytherapy for prostate cancer. Case 1 involved a 73-year-old man who had undergone LDR brachytherapy (145 Gy) for prostate cancer (prostate-specific antigen (PSA) 8.3 ng/mL, Gleason score 3+3=6, T2N0M0) in December 2009. He remained disease-free for eight years and four months, but later presented with anal pain and an anal mass. Biopsy confirmed SCC. Based on CT findings demonstrating perineal invasion, the clinical stage was determined as cT4N1bM0, with right obturator lymph node metastasis. Due to poor general condition, only diverting colostomy and external beam radiation therapy (EBRT, 70 Gy in 30 fractions) were performed. The patient died of aspiration pneumonia and sepsis on hospital day 94, in July 2018, eight years and seven months after the initial LDR treatment. Case 2 was a 61-year-old man with prostate cancer (PSA 6.1 ng/mL, Gleason score 3+5=8, T1N0M0) treated with LDR brachytherapy (110 Gy) combined with EBRT (45 Gy in 25 fractions) in July 2006. He remained disease-free for eight years and seven months, after which he developed anal pain in February 2015. Endoscopic biopsy confirmed anal canal SCC (T1N1M0). Laparoscopic abdominoperineal resection (Miles' operation) was performed, but local recurrence occurred one year later. Despite subsequent chemoradiation (5-fluorouracil plus mitomycin C) and systemic chemotherapy with XELOX (capecitabine plus oxaliplatin), the disease progressed, and he died in October 2016, 10 years and three months after the initial LDR treatment. Anal canal SCC is a rare malignancy, and its development following prostate cancer radiotherapy is extremely uncommon. These two cases may represent radiation-induced secondary cancers, underscoring the importance of long-term surveillance for secondary malignancies in patients undergoing prostate brachytherapy.