A Case of Human Epidermal Growth Factor Receptor 2‐Positive Colon Cancer With Invasive Micropapillary Carcinoma Component

A female patient in her 60s tested positive for the fecal occult blood test while undergoing health screening. Colonoscopy revealed a 15-mm-sized flat elevated lesion with a central depression in the sigmoid colon. Narrow-band imaging magnification revealed a Japan Narrow-Band Imaging Expert Team classification of type 2B, whereas crystal violet staining showed a mild to severely irregular type VI pit pattern. Ultra-magnification imaging revealed an EC3a morphology in the depressed area. Endoscopic ultrasonography revealed partial disruption of the third layer, leading to the diagnosis of T1b (SM) colon cancer. Owing to the intermediate lesion size and since the patient had requested it, an endoscopic submucosal dissection was performed as an initial treatment. Pathological analysis revealed a moderately differentiated tubular adenocarcinoma with an invasive micropapillary carcinoma (IMPC) component, with deep submucosal invasion. Additional surgery was performed, and no recurrence was observed in the following three years. IMPC is known for its high rate of lymph-node metastasis and poor prognosis, as reported for breast, bladder, and lung cancers. IMPC is rare; this report presents a literature review and case details. This case represents the first reported instance of identification of a cancerous IMPC component by magnifying endoscopy at the T1b (SM) depth. Thus, even for intermediate lesions, IMPC should be considered as a differential diagnosis when endoscopic imaging suggests malignancy.