This Phase 1b/2 trial will evaluate Hu5F9-G4 in combination with rituximab. Hu5F9-G4 is a monoclonal antibody which is designed to block a protein called CD47, which is widely expressed on human cancer cells. Blocking CD47 with Hu5F9-G4 may enable the body's immune system to find and destroy the cancer cells. Rituximab is a monoclonal antibody drug that is used for treatment of non-Hodgkin's lymphoma and other types of cancer.