Development and progression of colorectal cancer based on follow-up analysis.

Elucidating the pathway of colorectal cancer development and progression can lead to identification of lesions that must be treated appropriately. The aim of the present review was to summarize the development and progression of colorectal cancer based on radiological and endoscopic follow-up analyses. These studies revealed several characteristic findings, including that initial morphology with progression to advanced cancer was most commonly 0-Is, followed by 0-IIa. Based on the doubling time, 0-Ip grew slowly in comparison with other morphologies. The observation period from adenomas measuring <10 mm to intramucosal cancers was more than 5 years. This makes it difficult to draw any accurate conclusions about the natural history of colorectal cancer based on follow-up observation alone and it is difficult to exclude the selection bias because of the difficulty of follow up for flat and depressed tumor. However, the only reliable way to elucidate the natural history is to accumulate cases.