Circulating Tumor DNA MRD-Guided Adjuvant Therapy for Curatively Resected Locally Advanced Esophageal Squamous Cell Carcinoma

Inclusion Criteria: * 1\. Be willing and able to provide written informed consent. 2. Be ≥19 years of age on the day of signing the informed consent form. 3. Have ECOG performance status of 0 or 1 (Appendix 1). 4. Have a histologically confirmed diagnosis of squamous cell carcinoma of the esophagus * Patients with tumors of mixed histology (i.e., squamous and non-squamous) are eligible if the predominant histological component is squamous, except when small cell or neuroendocrine elements are present. 5\. Must have completed surgical resection for localized disease, either with prior neoadjuvant therapy (chemotherapy or chemoradiotherapy) or without prior neoadjuvant therapy (i.e., upfront surgery), in accordance with the 8th edition of the AJCC staging system (Appendix 2). Exceptionally, cases with supraclavicular lymph node metastasis as the only M1 lesion are also eligible if the lymph node has been surgically removed. 6\. Must have undergone curative surgery (R0 resection) with negative margins on the resected specimen. 7\. Complete resection must have been performed between 4-16 weeks before randomization. 8\. Must have a documented disease-free status based on a complete physical examination and imaging studies within 4 weeks before randomization. Imaging studies must include CT scans (or MRI) of the chest, abdomen, and pelvis. 9\. Must provide tumor tissue from pre-treatment biopsy (i.e., a biopsy obtained prior to neoadjuvant therapy in ca…