PRKCD and primary central nervous system lymphoma: Biallelic inactivation of thymocyte selection-associated high mobility group box (TOX) and protein kinase C-δ (PRKCD) genes is recurrently found in PCNSL, but not in systemic DLBCL, in addition to a high prevalence of myeloid differentiation primary response 88 (MYD88) mutation and cyclin-dependent kinase inhibitor 2 A (CDKN2A) biallelic loss17,18.