Advanced gastric antrum cancer

My father was diagnosed with advanced gastric antrum cancer recently. He took the surgery one week ago. The surgeon found it was advanced than expected. The pylorus is blocked, so food cannot go through it, and stuck in the stomach. The cancer has spread to the abdominal cavity and intestine mucous membrane. The surgeon could not do gastrectomy, he took out about 3000ml ascites and placed a tube from the esophagus to the colon to allow the food bypass the stomach.
About 2 days after the operation, my father got high-grade fever; it has lasted for 5 days.
My father is only 68, and this is a shock to my family. Could anyone give me any suggestion about the best method of treatment, either to let the fever down or the treatment for the cancer