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

To investigate the development and progression of colorectal carcinoma, sub mucosal invasive carcinoma (SMC) with residual intramucosal neoplasm was st udied histopathologically. Intramucosal neoplasm was confirmed by immunohis tochemical staining against anti-alpha-smooth muscle actin antibody. Submuc osal invasive carcinoma was classified into polypoid growth-type carcinoma (PGC) and non-polypoid growth-type carcinoma (NPGC), depending on the prese nce 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 mi nimal (invasion of the upper 500 mu m of the submucosal layer) in 52.9% of the PGC lesions. Conversely, 64.4% of NPGC lesions were less than or equal to 15 mm in size and the degree of submucosal invasion was moderate or seve re (Involving the middle and deeper layer of the submucosa) for 72.9% of NP GC. In other words, lesions of NPGC were significantly smaller in size but showed deeper infiltration than PGC lesions. Furthermore, PGC was derived f rom intramucosal polypoid carcinoma (including carcinoma with adenoma) and was morphologically identical to polyp cancer as reported previously. Howev er, NPGC was derived from the flat and/or depressed type of intramucosal ca rcinoma classified not as polyp type, but as the superficial type. Typical NPGC was, therefore, also of the superficial type. In addition, approximate ly 25% of PGC lesions were identified as having an adenoma-carcinoma sequen ce. There was no coexistence with adenoma in the NPGC lesions, suggesting d e novo development. When the degree of histologic atypia in the two types o f intramucosal carcinoma was compared, 74.7% of PGC lesions showed low-grad e carcinoma, regardless of tumor size, while 62.7% of NPGC lesions showed h igh-grade carcinoma in the intramucosal lesion. Approximately 25% of carcin omas with row-grade atypia were positive for p53 (as were the high-grade le sions), but it was not expressed in the adenoma. Therefore, tumor developme nt and the degree of invasion differed significantly between the two types of carcinoma.