Classification of advanced colorectal carcinomas by tumor edge morphology - Evidence for different pathogenesis and significance of polypoid and nonpolypoid tumors

BACKGROUND, Increasing evidence suggests that a substantial proportion of c olorectal carcinomas develop without a preexisting polypoid adenomatous les ion, but it is difficult to detect the possible origin of advanced carcinom as. The purpose of this study was to test the Validity and significance of a new histopathologic classification system based on the histologic analysi s of the tumor edge. METHODS, One hundred eighty-six unselected cases of colorectal carcinoma we re included. A new classification method to distinguish polypoid and nonpol ypoid growth type was based on the presence or absence of elevation of tumo r as compared with adjacent mucosa. Inter- and intraobserver agreement of c lassification was tested. Association with other clinicopathologic features including histopathologic characteristics of the tumors, presence or absen ce of lesional and concurrent adenoma, K-ras mutations, and prognosis was e valuated. RESULTS, Classification could be made in 75% of the tumors, and 25% were un classifiable, mostly due to absence of tumor margin in sections. Of the cla ssifiable carcinomas, 45% were classified as polypoid, of which 52% had les ional adenoma. Nonpolypoid tumors formed 48% of classifiable cases, and onl y 2% had lesional adenoma. Features of both polypoid and nonpolypoid carcin omas were present in 7% of cases. Concurrent extralesional adenomas were fo und more frequently in association with polypoid carcinomas. K-ras mutation s were more common in polypoid (43%) than in nonpolypoid tumors (8%; P = 0. 018). Nonpolypoid carcinomas were significantly (P = 0.03) more aggressive than polypoid carcinoma, with 38% and 20% recurrence rates, respectively. CONCLUSIONS. The authors' results indicate that advanced colorectal carcino mas can be classified according to growth pattern by observing the tumor ed ge. This classification has prognostic significance because nonpolypoid car cinomas appeared to have a worse prognosis than polypoid ones. (C) 2000 Ame rican Cancer Society.