The most common molecular alterations in PCNSL include mutations in MYD88 and CD79 and CDKN2A homozygous deletion.11 In a study of 39 PCNSL samples that were profiled using whole-genome sequencing, at the copy number level, PCNSL demonstrated significantly more CN losses in 6p21 (HLA-D locus) as well as recurrent losses in 9p21 (MTAP, CDKN2A/B) and 19p13 (CDKN2D) compared to DLBCL.12 In another study of 21 PCNSL samples that were analyzed using high-density single-nucleotide polymorphism, 9p21.3/CDKN2Acopyloss, was significantly more frequent in PCNSLs than in ABC-type DLBCLs. Here, CDKN2D is linked to primary central nervous system lymphoma.