Immune Indicator Model for Predicting Efficacy of PD-1 Monoclonal Antibody

This study is collecting blood samples from people with advanced esophageal squamous cell cancer (cancer of the food pipe) who are about to start a combination treatment of immunotherapy (a PD-1 antibody) and chemotherapy, in order to identify immune system markers in the blood that can predict whether this treatment will be effective. **You may be eligible if...** - You have confirmed stage IV esophageal squamous cell carcinoma (advanced cancer of the food pipe) - You are about to start treatment with a PD-1 immunotherapy antibody combined with chemotherapy **You may NOT be eligible if...** - You have an active autoimmune disease (such as lupus, rheumatoid arthritis, or inflammatory bowel disease) or one likely to return - You are currently receiving steroids or other immune-suppressing drugs - You are pregnant or breastfeeding - You have active serious infections Talk to your doctor to see if this trial is right for you.