A Phase II Study Evaluating an Organ Preservation Strategy Using Immune Checkpoint Blockade for Participants With Primary Colorectal or Gastroesophageal Cancer

Background: People with colorectal cancer (CRC) or gastroesophageal cancer (GEC) must often have major surgery to remove tumors from the esophagus, stomach, colon, or rectum. These surgeries can have adverse effects on their quality of life. Researchers want to know if one or two approved drugs (nivolumab with or without ipilimumab) can help people with CRC or GEC delay or avoid surgery. Objective: To test 1 or 2 drugs in people with CRC or GEC. Eligibility: People aged 18 years and older with CRC or GEC. People with GEC must also have changes in a particular gene. Design: Participants will visit the clinic about 15 times over the first 2 years. Each visit will last 4 to 8 hours. Participants will be screened. They will have a physical exam with blood and urine tests. They will have imaging scans. Small samples of tissue will be collected from their upper or lower digestive tract where the tumor is located. Both ipilimumab and nivolumab are administered through a tube attached to a needle inserted into a vein in the arm. Some participants will receive both drugs. Some will receive only nivolumab. Treatment will be given once every 3 weeks for up to 8 cycles up to (24 weeks). Participants will be evaluated every 6 weeks. Those who are responding well will continue with the drug treatments. If their disease progresses, they will go to surgery. After treatment ends, participants will have follow-up visits every 6 months for up to 5 years....