ALK and mature T-cell and NK-cell non-Hodgkin lymphoma: The 2016 World Health Organization classification defines 29 PTCL subtypes, including PTCL-not otherwise specified (PTCL-NOS), angioimmunoblastic T-cell lymphoma (AITL), anaplastic lymphoma kinase (ALK) positive anaplastic large cell lymphoma (ALK+ALCL), ALK negative ALCL (ALK-ALCL) and others (2).