A Granulation Polyp in the Colon Masquerading as Metastatic Cancer.

A 60-year-old Caucasian male was diagnosed with lung adenocarcinoma and multiple metastases to the bone, spleen, and brain. He underwent radiotherapy for the brain and lumbar spine metastases, plus chemotherapy (cisplatin and pemetrexed). The chemotherapy was discontinued due to vomiting and hyponatremia, and nivolumab was then administered. Eight months later, 18F-fluorodeoxyglucose positron emission tomography showed tracer uptake in the colon. Colonoscopy revealed a reddish multinodular polyp in the sigmoid colon. The polyp showed irregular microvessels. No colonic mucosal surface structures were observed. Colonic metastasis of the lung carcinoma was highly suspected; the polyp was therefore surgically removed. The histological analysis revealed granulation tissue and suppurative inflammation without neoplastic changes. We diagnosed the lesion as a granulation polyp. Despite the difficulty in diagnosing these lesions due to their rarity and similarity to metastatic colon tumors, we suggest that recognizing the endoscopic features of the polyp surface may allow a preoperative diagnosis.