ALK and anaplastic large cell lymphoma: Based on ALK expression and clinical context, ALCL is divided into four main entities: systemic ALK-positive ALCL, systemic ALK-negative ALCL, primary cutaneous ALCL (pcALCL) and breast implant-associated ALCL (BIA-ALCL). ALK-positive ALCL arises from genetic rearrangements involving the ALK gene located on chromosome 2p23, most commonly the t(2;5)(p23;q35) translocation, which fuses ALK with the nucleophosmin (NPM) gene.