Condition of muscularis mucosae is a risk factor for lymph node metastasis in T1 colorectal carcinoma.

Background: The Japanese Society for Cancer of the Colon and Rectum Guidelines for the Treatment of Colorectal Cancer 2010 state that curable T1 colorectal carcinoma (CRC) after endoscopic resection shows favorable histologic grade, absence of vessel involvement, submucosal invasion depth of <1,000 μm, and low-grade tumor budding.

Methods: We evaluated 322 consecutive T1 CRCs with LN dissection between January 1993 and March 2012. According to the muscularis mucosae condition, CRCs were classified into three groups: type A, clearly identified; type B, incompletely disrupted with deformity; or type C, completely disrupted. We examined the relationship between the muscularis mucosae condition, clinicopathological findings, and lymph node (LN) metastasis.

Results: The overall incidence of LN metastasis was 11.8 % (38/322): 0 % (0/46) for the type A group, 7.2 % (7/97) for the type B group, and 17.3 % (31/179) for the type C group. In univariate analysis of type B and C groups, unfavorable histologic grade, submucosal invasion of ≥1,000 μm, positive lymphatic invasion, high-grade tumor budding, and the type C group were associated with a significantly higher incidence of LN metastasis. In multivariate analysis, high-grade tumor budding (P < 0.001, odds ratio [OR] = 4.86), unfavorable histologic grade (P = 0.026, OR = 4.83), positive lymphatic invasion (P < 0.001, OR = 4.17), and the type C group (P = 0.012, OR = 3.38) were significantly associated with LN metastasis. The type C group showed a high incidence of moderate/severe lymphatic invasion.

Conclusions: The condition of the muscularis mucosae was an indicator of LN metastasis in T1 CRC.