Of great clinical importance, the MCD/C5/MYD88 molecular subtype identified in systemic DLBCL has been associated with the worst clinical outcomes out of all the molecular subtypes [43], and other studies have reinforced the longstanding clinical observation of a worse prognosis of PCNSL as compared to extracerebral DLBCL [1,2]. The gene discussed is MYD88; the disease is primary central nervous system lymphoma.