Delayed response in ipilimumab therapy.

Metastatic melanoma is a deadly disease with a 5-year survival rate lower than 20%. In 2011, ipilimumab, a fully humanized antibody that binds to cytotoxic T-lymphocyte-associated antigen 4 (CTLA4) was approved by the US Food and Drug Administration based on improved survival in a pivotal trial. CTLA4 is a molecule on cytotoxic T-lymphocytes that plays a critical role in attenuating immune responses. Ipilimumab blocks the binding of B7, the ligand of CTLA4, thereby blocking the activation of CTLA4 and sustaining antitumor immune responses. The time course to response can be variable with immunotherapeutics. We report on a patient who experienced a considerable delay before responding to ipilimumab.