Peritoneal mesothelioma with invasion of the urinary bladder 20 years post radiation therapy for colon adenocarcinoma

We present the case of a 66-year-old male with a history of iatrogenic bladder injury and radiation therapy for colon adenocarcinoma 20 years prior. A computed tomography of the thorax, abdomen and pelvis, reported a presacral mass with invasion to the bladder, ureters and lymph nodes. An initial bladder biopsy was histologically inconclusive. A later biopsy taken during emergency bypass surgery for small bowel obstruction, while the patient was positive for coronavirus disease of 2019, concluded that the mass was a peritoneal mesothelioma of epithelioid origin. The combination management of cytoreductive surgery with intraperitoneal chemotherapy has been a near universal standard of care for epithelioid peritoneal mesothelioma provided that the patient is an appropriate candidate for surgical interventions. To the best of our knowledge, this is the first case report of malignant peritoneal mesothelioma as a second primary carcinoma, many years after exposure to radiation therapy for colon adenocarcinoma.