ALK and mature T-cell and NK-cell non-Hodgkin lymphoma: The most commonly observed subtypes are the so-called PTCL not otherwise specified (PTCL NOS), the T-follicular helper-related PTCL, angioimmunoblastic type (AITL) and the anaplastic large cell lymphomas (ALCL), and anaplastic kinase-negative (ALK−) or positive (ALK+).