A case report of rectal squamous cell carcinoma following radiation therapy for prostate cancer: a management dilemma.

Introduction: Rectal squamous cell carcinoma (rSCC) is exceedingly rare and lacks guidelines for staging or management. Prior radiation is a known risk factor for colorectal adenocarcinomas, but has rarely been reported with rSCC, with solid organ tumors generally arising after about 10 years following radiation. It poses a management dilemma as reradiation is associated with risks, but the outcome in patients without radiation therapy in rSCC is scarce. Case Description: We present a 76-year-old male with a past medical history of prostate adenocarcinoma treated with external beam radiotherapy 7 years prior, who presented with bright red bleeding per rectum and was diagnosed with tumor, node, and metastasis (TNM) stage IIIB rSCC. He underwent abdominal perineal resection (APR) and 4 cycles of adjuvant chemotherapy with carboplatin with paclitaxel. Radiotherapy was not done due to concern for complications with a history of prior radiation within the same region. On a 3-month follow-up, he was without recurrence, but passed away shortly after due to respiratory failure from severe mitral regurgitation. Conclusions: Radiation-associated rSCC and its management are rare and complex. Staging based on rADC as opposed to anal squamous cell carcinoma (aSCC) seems more intuitive based on location, but the choice of systemic treatment should be aSCC-based, given similar histology. A streamlined guideline on staging and management would be beneficial to track outcomes in rSCC, given its rarity, and would benefit from a consensus.