Diminutive intramucosal invasive (Tis) sigmoid colon carcinoma.

A 60-year-old woman underwent colonoscopy, which revealed a red, 5-mm protruded lesion in the sigmoid colon, surrounded by white spots in white-light imaging. Indigo carmine spray indicated endoscopic morphological type Is + IIc. The vessel pattern was diagnosed as JNET-type 2B in magnifying narrow-band imaging, and magnified crystal violet-stained images revealed a VI low-grade pit pattern. We endoscopically diagnosed this lesion as an intramucosal or slightly invasive submucosal carcinoma with low confidence, and performed endoscopic mucosal resection to obtain a total biopsy. Hematoxylin and eosin staining of the resected specimen showed that the surface of the lesion was well-differentiated adenocarcinoma. The muscularis mucosae was identified by desmin immunostaining. There was no lymphovascular infiltration. Structural atypia was notable in the invasive front, indicating well-to-moderately differentiated adenocarcinoma, which invaded the lamina muscularis mucosae. In addition, desmoplastic reaction was recognized to be present. The lesion was, therefore, diagnosed as an intramucosal invasive (Tis) carcinoma, rather than high-grade dysplasia, according to the World Health Organization definition.