Standard of Care Alone or in Combination With Ad-CEA Vaccine and Avelumab in People With Previously Untreated Metastatic Colorectal Cancer QUILT-2.004

Background: Colorectal cancer is a common cancer in the Unites States (U.S.) It causes the second most cancer-related deaths. The drug avelumab and vaccine Ad-CEA together help the immune system fight cancer. Objective: To test if avelumab and Ad-CEA plus standard therapy treats colorectal cancer that has spread to other sites better than standard therapy alone. Eligibility: People ages 18 and older with untreated colorectal cancer that has spread in the body Design: Participants will be screened with: Test to see if their cancer has a certain deficiency Blood, urine, and heart tests Scans Medical history Physical exam Tumor sample. This can be from a previous procedure. A small group of participants will get Ad-CEA and avelumab plus standard therapy. This is leucovorin calcium (folinic acid), fluorouracil, and oxaliplatin (FOLFOX) plus bevacizumab for up to 24 weeks then capecitabine plus bevacizumab. The others will have treatment in 2-week cycles. They will be Arm A or B: Arm A: FOLFOX and bevacizumab by intravenous (IV) days 1 and 2 for 12 cycles. After that, capecitabine by mouth twice a day and bevacizumab by IV on day 1. Arm B: Ad-CEA injection every 2-12 weeks. Avelumab by IV on day 1 of each cycle. FOLFOX and bevacizumab by IV days 2 and 3 for 12 cycles. Then, capecitabine by mouth twice a day and bevacizumab through IV on day 2. Participants will repeat screening tests during the study. Participants will be treated until their disease gets worse or they have bad side effects. Arm A participants can join Arm B. They will have a visit 4 5 weeks after they stop therapy.