Outcomes of noncurative endoscopic submucosal dissection for T1 colorectal cancer: Prospective, multicenter, cohort study in Japan

Objectives This study investigated the incidence of lymph node metastasis and long‐term outcomes in patients with T1 colorectal cancer where endoscopic submucosal dissection (ESD) resulted in noncurative treatment. It is focused on those with deep submucosal invasion, a factor considered a weak predictor of lymph node metastasis in the absence of other risk factors. Methods This nationwide, multicenter, prospective study conducted a post‐hoc analysis of 141 patients with T1 colorectal cancer ≥20 mm where ESD of the lesion resulted in noncurative outcomes, characterized by poor differentiation, deep submucosal invasion (≥1000 μm), lymphovascular invasion, high‐grade tumor budding, or positive vertical margins. Clinicopathologic features and patient prognoses focusing on lesion sites and additional surgery requirements were evaluated. Lymph node metastasis incidence in the low‐risk T1 group, identified by deep submucosal invasion as the sole high‐risk histological feature, was assessed. Results Lymph node metastasis occurred in 14% of patients undergoing additional surgery post‐noncurative endoscopic submucosal dissection for T1 colorectal cancer. In the low‐risk T1 group, in the absence of other risk factors, the frequency was 9.7%. The lymph node metastasis rates in patients with T1 colon and rectal cancers did not differ significantly (14% vs. 16%). Distant recurrence was observed in one patient (2.3%) in the ESD only group and in one (1.0%) in the additional surgery group, both of whom had had rectal cancer removed. Conclusion The risk of lymph node metastasis or distant occurrence was not negligible, even in the low‐risk T1 group. The findings suggest the need for considering additional surgery, particularly for rectal lesions (Clinical Trial Registration: UMIN000010136).