Original contributionIntramucosal colorectal carcinoma with invasion of the lamina propria: a study by the Japanese Society for Cancer of the Colon and Rectum

- Invasive cancers represented 5.1% of intramucosal dysplastic/neoplastic lesions.
- Invasion of small cell clusters is an objective criterion of intramucosal invasion.
- Stromal response is not a useful criterion for diagnosis of intramucosal invasion.
- We suggest that intramucosal colorectal carcinomas be staged pT1a.

SummaryCancer invasion of the lamina propria is an important pathological finding. However, the clinicopathologic features and diagnostic accuracy of intramucosal carcinoma assessment in colorectal carcinoma (CRC) are unknown. In this study, intramucosal CRCs were reviewed in institutions affiliated with the Japanese Society for Cancer of the Colon and Rectum, and 32 cases with invasion of the lamina propria were identified. Next, a consensus meeting was held to select cases with a high consensus about the presence of invasion, which were reviewed by one Western pathologist for confirmation. In addition to clinicopathologic evaluation, concordance was assessed for diagnosis and histologic findings. During the consensus meeting, 3 cases were found to show ambiguous features such that it was unclear whether there was intramucosal or submucosal invasion, and 7 cases were judged to have invasion of the lamina propria by more than 75% of the pathologists. A poorly differentiated adenocarcinoma and a signet ring cell carcinoma were diagnosed unanimously. Concordance in diagnosis and detection of characteristics of invasion of the lamina propria proved to be only poor to fair. Single or small clusters of cells and atypical or complex glandular arrangements that are beyond normal mucosal architecture were detected more frequently in the 7 high-consensus tumors. Desmoplasia and marked inflammation were detected more often in cases characterized as ambiguous. Intramucosal CRCs with invasion of the lamina propria constituted 5.1% of the surgically resected high-grade intramucosal epithelial dysplastic/neoplastic lesions, and stromal infiltration of single or small clusters of cells is the best objective criterion of invasion.