We propose that the term “PCNSL” should be reserved for the most common (and probably only) molecular subtype of PCNS-DLBCL, namely, PCNS-DLBCL with MYD88 and B cell receptor (BCR) signaling pathway mutations, which is nowadays described as the MCD/C5/MYD88 molecular group (see below). The gene discussed is MYD88; the disease is diffuse large B-cell lymphoma.