Growth and development of colorectal cancer with subclassification on submucosa and proper muscle infiltrating cancer

Colorectal cancer (CRC) infiltrating the submucosa (sm cancer) and the proper muscle (mp cancer) represent an early and an intermediate stage in the development of CRC, and sm and mp cancer are therefore appropriate to discuss the natural history of CRC. A total of 337 sm cancers and 291 mp cancers resected in our series were evaluated. We divided sm and mp cancers into three categories, respectively, sm 1, sm 2, sm 3, mp 1, mp 2, and mp 3, according to the depth of infiltration of the submucosa or the proper muscle. The deeper the invasion, the larger of the tumor size, and the proportion of depressed type in their configuration increases. On the contrary, the proportion of tumors with adenomatous component decreases. A larger proportion of tumors in all categories of infiltration showed PG more of ten than that of NPG in their marginal structure. In this study, 17% of sm cancer and 23% of mp cancer might develop not via the adenoma-carcinoma sequence.