Histologic and immunohistochemical analysis of early submucosal invasive carcinoma of the colon and rectum.

To investigate the development and progression of colorectal carcinoma, submucosal invasive carcinoma (SMC) with residual intramucosal neoplasm was studied histopathologically. Intramucosal neoplasm was confirmed by immunohistochemical staining against anti-alpha-smooth muscle actin antibody. Submucosal invasive carcinoma was classified into polypoid growth-type carcinoma (PGC) and non-polypoid growth-type carcinoma (NPGC), depending on the presence of intramucosal tumor proliferation. Tumors were > 15 mm in size in 78.2% of the PGC lesions studied, but the degree of submucosal invasion was minimal (invasion of the upper 500 microm of the submucosal layer) in 52.9% of the PGC lesions. Conversely, 64.4% of NPGC lesions were 15 mm in size and the degree of submucosal invasion was moderate or severe (involving the middle and deeper layer of the submucosa) for 72.9% of NPGC. In other words, lesions of NPGC were significantly smaller in size but showed deeper infiltration than PGC lesions. Furthermore, PGC was derived from intramucosal polypoid carcinoma (including carcinoma with adenoma) and was morphologically identical to polyp cancer as reported previously. However, NPGC was derived from the flat and/or depressed type of intramucosal carcinoma classified not as polyp type, but as the superficial type. Typical NPGC was, therefore, also of the superficial type. In addition, approximately 25% of PGC lesions were identified as having an adenoma-carcinoma sequence. There was no coexistence with adenoma in the NPGC lesions, suggesting de novo development. When the degree of histologic atypia in the two types of intramucosal carcinoma was compared, 74.7% of PGC lesions showed low-grade carcinoma, regardless of tumor size, while 62.7% of NPGC lesions showed high-grade carcinoma in the intramucosal lesion. Approximately 25% of carcinomas with low-grade atypia were positive for p53 (as were the high-grade lesions), but it was not expressed in the adenoma. Therefore, tumor development and the degree of invasion differed significantly between the two types of carcinoma.