Treatment Decision for Locally Resected T1 Colorectal Carcinoma-Verification of the Japanese Guideline Criteria for Additional Surgery Based on Long-Term Clinical Outcomes.

INTRODUCTION: To verify the value of the pathological criteria for additional treatment in locally resected pT1 colorectal carcinoma (CRC) which have been used in the Japanese Society for Cancer of the Colon and Rectum (JSCCR) guidelines since 2009.

METHODS: We enrolled 4,719 patients with pT1 CRC treated at 27 institutions between July 2009 and December 2016 (1,259 patients with local resection alone [group A], 1,508 patients with additional surgery after local resection [group B], and 1,952 patients with surgery alone [group C]). All 5 factors of the JSCCR guidelines (submucosal resection margin, tumor histologic grade, submucosal invasion depth, lymphovascular invasion, and tumor budding) for lymph node metastasis (LNM) had been diagnosed prospectively.

RESULTS: Any of the risk factors were present in 3,801 patients. The LNM incidence was 10.3% (95% confidence interval 9.3-11.4) in group B/C patients with risk factors, whereas it was 1.8% (95% confidence interval 0.4-5.2) in those without risk factors ( P < 0.01). In group A, the incidence of recurrence was 3.4% in patients with risk factors, but it was only 0.1% in patients without risk factors ( P < 0.01). The disease-free survival rate of group A patients classified as risk positive was significantly worse than those of groups B and C patients. However, the 5-year disease-free survival rate in group A patients with no risk was 99.2%.

DISCUSSION: Our large-scale real-world multicenter study demonstrated the validity of the JSCCR criteria for pT1 CRC after local resection, especially regarding favorable outcomes in patients with low risk of LNM.