Peripheral T-cell lymphoma (PTCL) is a complex and heterogeneous type of non-Hodgkin lymphoma whose classification is divided in PTCL-not otherwise specified (PTCL-NOS), angio-immunoblastic T-cell lymphoma (AITL) and anaplastic large cell lymphoma (ALCL) with or without anaplastic lymphoma kinase genetic abnormalities (ALK+ ALCL and ALK− ALCL) and other less common subtypes. The gene discussed is ALK; the disease is anaplastic large cell lymphoma.