Although numerous therapies to induce tumor‐specific immune responses, such as peptide therapy, dendritic cell therapy, and tumor‐infiltrating lymphocyte therapy, as well as therapies to enhance nonspecific immune responses with interleukin 2 and interferons, have been attempted, no immunotherapy had been proven effective in phase 3 trials until the advent of ipilimumab, an anti‐cytotoxic T lymphocyte‐associated antigen 4 (CTLA‐4) antibody (Ab).2, 3. The gene discussed is CTLA4; the disease is neoplasm.