Risk of metastatic recurrence after endoscopic resection for esophageal squamous cell carcinoma invading into the muscularis mucosa or submucosa: a multicenter retrospective study.

Background We aimed to elucidate the risk of metastatic recurrence after endoscopic resection (ER) without additional treatment for esophageal squamous cell carcinomas (ESCCs) with tumor invasion into the muscularis mucosa (pT1a-MM) or submucosa (T1b-SM). Methods We retrospectively enrolled patients with pT1a-MM/pT1b-SM ESCC after ER at 21 institutions in Japan between 2006 and 2017. We compared metastatic recurrence between patients with and without additional treatment, stratified into category A (pT1a-MM with negative lymphovascular invasion [LVI] and vertical margin [VM]), B (tumor invasion into the submucosa ≤ 200 µm [pT1b-SM1] with negative LVI and VM), and C (others). Subsequently, using multivariate Cox analysis, we evaluated risk factors for metastatic recurrence after ER without additional treatment. Results We enrolled 593 patients, and metastatic recurrence occurred in 38 patients. Metastatic recurrence after additional treatment was significantly lower than that after no additional treatment in category C (9.1% vs. 23.6% in 5 years, p = 0.001), whereas no significant difference was noted in categories A (0.0% vs. 2.6%) and B (0.0% vs. 4.3%). In patients without additional treatment after ER, risk factors for metastatic recurrence were lymphatic invasion (hazard ratio [HR], 5.61), positive VM (HR, 4.55), and tumor invasion into the submucosa > 200 μm (HR, 3.25), and, but near half of the patients with metastatic recurrence had no further recurrence after salvage treatment, resulting in excellent 5-year disease-specific survival in categories A (99.6%) and B (100.0%). Conclusions Closed follow-up with no additional treatment may be an acceptable option after ER in pT1a-MM/pT1b-SM1 ESCC with negative LVI and VM.