TNFRSF8 and anaplastic large cell lymphoma: The introduction of CD30 into immunohistochemical diagnostic pathology has led to the definition of anaplastic large cell lymphoma (ALCL) as an entity, to a more precise subtyping of peripheral T‐cell lymphoma (PTCL), to the elucidation of the cellular origin of Hodgkin and Reed‐Sternberg (HRS) cells, and to the understanding of their special features.