A case of tubulovillous adenoma with neuroendocrine cell nest resection

An 80-year-old man underwent a colonoscopy after PET-CT for pulmonary squamous cell carcinoma (cT3N0M0, stage IIB) showed rectal uptake, revealing a 20-mm 0-IIa lesion (Rb). However, the lung cancer treatment was prioritized. Eight months later, another colonoscopy showed lesion progression to 25 mm (0-IIa+Is), and an en bloc endoscopic submucosal dissection was performed. Histological examination revealed a high-grade tubulovillous adenoma with <5% neuroendocrine cell nests confined to the lamina propria. These findings were consistent with composite intestinal adenoma-microcarcinoid, a rare mucosa-confined lesion with a favorable prognosis that is typically identified incidentally on pathological examination.