A 56-year-old man with a history of hypertension and hyperlipidemia was referred by gastroenterology for bleeding per rectum. Because of a family history of colon cancer, he had several prior colonoscopies, most recently 3 years ago, without evidence of pathology. His mother was diagnosed with colon cancer in her mid-40s. His current colonoscopy demonstrated a 2.4 × 1.5 cm cecal adenocarcinoma. Staging workup revealed no evidence of metastatic disease. Because of the patient’s family history, the specimen was further evaluated and found to have high microsatellite instability (MSI-H). The patient was referred to a genetic counselor and found to have a germline pathogenic variant in MSH6 on gene panel testing. The patient did not have a family history of any extracolonic malignancies.
The patient underwent an uncomplicated laparoscopic total abdominal colectomy with ileorectal anastomosis, which revealed a T2N0Mx adenocarcinoma with abundant peritumoral lymphocytes. He was discharged on postoperative day 2, and recuperated appropriately from surgery. Follow-up surveillance proctoscopy showed no evidence of disease. His sole offspring, a 25-year-old man, was negative for a pathogenic variant in MSH6 and had no polyps on colonoscopy. His siblings did demonstrate a pathogenic variant in MSH6 and are currently opting for annual surveillance colonoscopy.