The most common molecular alterations in PCNSL include mutations (MYD88 and CD79) and CDKN2A homozygous deletion.11 In addition, CN losses in 6p21 (HLA-D locus) as well as recurrent losses in 9p21 (MTAP, CDKN2A/B) and 19p13 (CDKN2D) are more common in comparison to DLBCL.12 We sought to assess the effect of CDKN2A homozygous deletion on sensitivity to induction chemotherapy. This evidence concerns the gene MTAP and primary central nervous system lymphoma.