We are enrolling people who have had complete surgical removal of a stage II or stage III colorectal cancer. We will draw blood samples for circulating tumor DNA (ctDNA) to find out if this blood test can be used to detect recurrence of the cancer. People will be followed for at least 3 years and up to 5 years.

We are studying how well combination chemotherapy, bevacizumab, and/or atezolizumab work in treating people with deficient deoxyribonucleic acid (DNA) mismatch repair colorectal cancer that has spread from where it first started (primary site) to other places in the body (metastatic). Chemotherapy drugs, such as fluorouracil, oxaliplatin, and leucovorin calcium, work in different ways to stop the growth of tumor cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. Bevacizumab may stop or slow colorectal cancer by blocking the growth of new blood vessels necessary for tumor growth. Immunotherapy with monoclonal antibodies, such as atezolizumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. Giving combination chemotherapy, bevacizumab, and atezolizumab may work better in treating patients with colorectal cancer.