Epstein–Barr virus latent membrane protein 1 (LMP1) is an Epstein–Barr virus (EBV) protein that regulates its own expression and the expression of human genes. It has a molecular weight of approximately 63 kDa, and its expression induces many of the changes associated with EBV infections and activation of primary B cells. LMP1 is the best-documented oncoprotein of the EBV latent gene products, as it is expressed in most EBV-related human cancers such as the various malignant Epstein-Barr virus-associated lymphoproliferative diseases.