ALK and mature T-cell and NK-cell non-Hodgkin lymphoma: Peripheral T-cell lymphoma (PTCL) is a heterogeneous malignancy that is relatively rare, accounting for ~10% of all non-Hodgkin lymphomas (NHLs) in Western populations.1 The most common subtypes of PTCL are the so-called ‘nodal’ PTCLs: PTCL-not otherwise specified (PTCL-NOS), angioimmunoblastic T-cell lymphoma (AITL), and systemic anaplastic large cell lymphoma (sALCL).1 sALCL is subdivided into those that harbor a chromosomal translocation involving the anaplastic lymphoma kinase (ALK) gene, called ALK-positive (ALK+) sALCL, and those that do not (ALK-negative, ALK−).