- Part I (patients with prostate or colon cancer or follicular or mantle cell lymphomas) (prostate cancer and mantle cell lymphoma closed to accrual as of 3/10/2005; colon cancer closed to accrual as of 9/28/05): Patients receive anti-cytotoxic T-lymphocyte-associated antigen-4 monoclonal antibody (MDX-CTLA4) IV over 90 minutes on day 1. Treatment repeats every 28 days for 4 courses in the absence of disease progression or unacceptable toxicity.