The relative incidence of CNS disease at first relapse/progression based on tumor histology was 5% (n = 4) for PTCL, not otherwise specified (NOS), 17% (n = 2) for ALK + ALCL, and 8% (n = 2) for ALK-negative ALCL (ALK- ALCL). Here, ALK is linked to mature T-cell and NK-cell non-Hodgkin lymphoma.