A three-tier classification system based on the depth of submucosal invasion and budding/sprouting can improve the treatment strategy for T1 colorectal cancer: a retrospective multicenter study.

More than 85% of patients with T1 colorectal cancer have no lymph node metastasis and can be cured by endoscopic resection. To avoid unnecessary surgery after complete endoscopic resection, accurate histologic methods for evaluating resected specimens are needed to discriminate those at high risk for lymph node metastasis. A retrospective multi-institutional, cross-sectional study of 806 T1 colorectal cancer patients was conducted. A budding/sprouting score was incorporated for predicting lymph node metastasis in addition to other parameters, including the depth of submucosal invasion, histologic grade, and lymphovascular invasion. Lymph node metastasis was detected in 97 patients. Independent predictors of lymph node metastasis by multivariate analysis were depth of submucosal invasion ≥1000 μm (odds ratio (95% confidence interval)=5.56 (2.14-19.10)) and high-grade budding/sprouting (3.14 (1.91-5.21)). Among lesions with a depth of submucosal invasion ≥1000 μm, lymph node metastasis was detected in 59 (29%) of 207 patients with high-grade budding/sprouting, and in 34 (9%) of 396 with low-grade budding/sprouting. Lymph node metastasis was detected in only 4 (2%) of 203 lesions with a depth of submucosal invasion <1000 μm. Of these four tumors, three invaded lymphatic and/or venous vessels. Thus, the risk for lymph node metastasis can be classified into three groups: high risk with a depth of submucosal invasion ≥1000 μm and high-grade budding/sprouting, intermediate-risk with a depth of submucosal invasion ≥1000 μm and low-grade budding/sprouting, and low-risk with a depth of submucosal invasion <1000 μm. These findings revealed that a depth of submucosal invasion ≥1000 μm and high-grade budding/sprouting are powerful predictive parameters for lymph node metastasis in T1 colorectal cancer. This three-tier risk classification system will facilitate the decision for additional major surgery for T1 colorectal cancer patients after successful endoscopic treatment.