A 66-year-old male with positive fecal occult blood test underwent conventional colonoscopy, which revealed a 10 mm 0-Is lesion with a slightly depressed area in the sigmoid colon. Three days later, the second endoscopic examination revealed that the depressed area had developed well-demarcated and deeper, and microsurface structure could not be evaluated due to erosion on the depressed surface. However, the conventional images and morphological changes of the lesion strongly suggested T1b colorectal cancer with rapid growth. Fourteen days after detection, just before the laparoscopic surgery, the third examination revealed that the depressed area had become much deeper with increased thickness of the elevated margin, and a VI high-grade pit pattern was observed on the depressed surface with exposure of the submucosal cancer mass. Histological examination revealed submucosal massive invasion (2800 μm) of moderately differentiated tubular adenocarcinoma and lymph node metastasis (N1). Some T1b cancers develop rapid morphological changes in a short period of time. In those cases, we should perform surgery even for T1b cancers as soon as possible.
