ALK(–)ALCL is molecularly distinct from PTCL-NOS and ALK(+)ALCL. (A) A unique gene expression signature for ALCL was identified and then ALK(+)ALCL cases were separated from ALK(–)ALCL (reclassified ALCL cases are indicated at the top). (B) Representative gene signatures/pathway enriched in ALK(+)ALCL compared with ALK(–)ALCL. (C) A representative re-classified ALCL case (hematoxylin and eosin staining [H&E]) with a pathological diagnosis of PTCL-NOS showing expression of CD30, GZMB, and TIA, but no expression of ALK by immunostaining.