Patients with oligometastases show distant relapse in only a limited number of regions. Local therapy such as surgical resection, radiotherapy, chemoradiotherapy, and radiofrequency ablation for the relapsed sites may thus improve patient survival. Oligometastases are divided into oligo-recurrence and sync-oligometastases. Oligo-recurrence indicates a primary lesion that is controlled, and sync-oligometastases indicate a primary lesion that is not controlled. The management of oligo-recurrence and sync-oligometastases in esophageal squamous cell carcinoma has not been clearly established, and treatment outcomes remain equivocal. We reviewed 14 articles, including three phase II trials, that were limited to squamous cell carcinoma. Multimodal treatment combining surgical resection and chemoradiotherapy for oligo-recurrence of esophageal squamous cell carcinoma appears to be a promising treatment. With the development of more effective chemotherapy and regimens that combine immune checkpoint inhibitors, it will become more likely that sync-oligometastases that were unresectable at the initial diagnosis can be brought to conversion surgery. Currently, a randomized, controlled phase III trial is being conducted in Japan to compare a strategy for performing definitive chemoradiotherapy and, if necessary, salvage surgery with a strategy for conversion surgery in patients who can be resected by induction chemotherapy.
Keywords: conversion surgery; distant metastases; esophageal cancer; local therapy; multimodal therapy; oligo-recurrence; oligometastases; squamous cell carcinoma; sync-oligometastases; systemic therapy.