Deregulation of COX-2 has been implied in the pathogenesis of several cancers, in particular colorectal cancer, where it impacts on oncogenic signaling, invasion and metastasis, survival and angiogenesis.12, 13, 14, 15 Moreover, COX-2-dependent prostaglandin release can suppress antigen presentation and immune activation in cancer.16 Here we describe COX-2 as a suppressor of antigen-induced interferon-gamma secretion of T cells and inducer of immunosuppressive factors that contributes to escape from immune surveillance and resistance to cellular immunotherapy. The gene discussed is PTGS2; the disease is cancer.