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lance colonoscopy, which revealed a flat elevated polyp (IIa), about 5mm in diameter, in the cecum (●" Fig. 1). A second colonoscopy (2 years later) showed a flat elevated polyp with a mild depression, about5mmindiameter(IIa+IIc) (●" Fig. 2). Athirdcolonoscopy(3years later) revealed a faintly reddish depressed lesion (IIc), about 9mm in diameter (●" Fig. 3a,b). Magnifying chromoendoscopy showed a type VI pit pattern (Kudo classification) in the depression (●" Fig. 3c). Endoscopic resection was carried out for histological evaluation. Histologically, the resected specimenwas composed of well tomoderately differentiated adenocarcinomawithout any adenomatous components, which had infiltrated superficially into the submucosal layer along with lymphatic invasion (●" Fig. 4). Laparoscopy-assisted colectomy was thereafter carried out with curative intent. Histologically, no locally residual tumor or lymph node metastasis wasdetected. A few retrospective analyses using radiographic imageshavedemonstrated the development of colorectal tumors [1–3]; however, the progression of nonpolypoid cancer, especially the depressed type, still remains obscure. Through retrospective analysis of endoscopic images [4], the present case showed remarkablemorphological changes. We hypothesized that the initial lesion could be an adenomatous polyp, that the mild depressed area at the second examination was cancerous, and that the cancerous depressed area gradually replaced the surrounding flat adenoma horizontally and invaded the submucosal layer vertically. The doubling time of this lesion should be 6.3 months, therefore, based on the growth rate of colorectal cancers reported in a retrospective study [2], this lesion can be considered to have rapidly developed from a mucosal lesion into a submucosal cancer with lymphatic invasion at even as small a size as 9mm. As the natural history of nonpolypoid cancer, especially during the process of the initial shift from the colorectal mucosa to the submucosa, has not yet been fully elucidated, the present report is invaluable because it demonstrates the progression of the lesion using colonoscopy. Natural progression of a nonpolypoid colon cancer: endoscopic morphological changes over 3 years