Minimally Residual of Esophageal Cancer 001

This study is examining the use of a blood test that detects circulating tumor DNA (ctDNA) to monitor treatment response in patients with esophageal squamous cell cancer (ESCC) who are receiving chemotherapy, immunotherapy, and radiation. The goal is to see if these blood-based markers can better predict who will respond to treatment or relapse. **You may be eligible if...** - You are 18 to 75 years old with confirmed Stage II or III esophageal squamous cell cancer - Your cancer is not suitable for surgery - You are receiving the planned treatment regimen (neoadjuvant immunochemotherapy followed by chemoradiation with immunotherapy, then maintenance immunotherapy) - Your overall health and organ function are adequate (ECOG 0-1) **You may NOT be eligible if...** - You have been treated for another cancer in the past 5 years - Your esophageal cancer is of a different cell type (adenocarcinoma or mixed type) - You have uncontrolled systemic diseases (heart failure, active infection, uncontrolled high blood pressure) - You have active autoimmune disease or have previously received certain immunotherapy drugs - You are HIV positive - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.