Synchronous Rectal and Prostate Adenocarcinoma: A Rare Clinical Dilemma

A BSTRACT Synchronous adenocarcinomas of the rectum and prostate are rare, especially in the absence of an underlying genetic predisposition. Their anatomical proximity and differing therapeutic protocols pose a sequencing dilemma, as prioritization of one malignancy may delay the optimal management of the other and increase the risk of disease progression or treatment-related toxicity. A 79-year-old male presented with frequent loose stools mixed with blood and mucus. Positron emission tomography–computed tomography demonstrated distinct fluorodeoxyglucose-avid lesions in the rectum (maximum standardized uptake value [SUV max ]: 15.6) and prostate (SUV max : 23.19). Colonoscopic biopsy confirmed moderately differentiated rectal adenocarcinoma. Serum prostate-specific antigen was elevated at 56.35 ng/mL, and prostate biopsy confirmed acinar adenocarcinoma. To address sequencing challenges, androgen deprivation therapy (ADT) was initiated for prostate cancer, followed by abdominoperineal resection with end colostomy for rectal cancer. Definitive prostate radiotherapy and adjuvant rectal radiotherapy were delivered concurrently using intensity-modulated radiotherapy (IMRT) to prevent field overlap and dosimetric errors. Adjuvant chemotherapy for rectal cancer was subsequently administered, alongside continued ADT. At 1-year follow-up, the patient remained disease-free. This case demonstrates that synchronous rectal and prostate adenocarcinomas can be effectively managed through careful diagnostic confirmation and individualized treatment sequencing. The use of modern radiation techniques, such as concurrent IMRT, allows safe and precise dose delivery to both pelvic sites, enabling timely multimodality treatment when minimizing toxicity. Early multidisciplinary planning is essential for achieving favorable outcomes in such complex clinical scenarios.