ALK and anaplastic large cell lymphoma: However, PTCL remains extremely difficult to treat, because most PTCL subtypes become refractory to even aggressive chemotherapy regimens or relapse, with the exception of anaplastic lymphoma kinase-positive anaplastic large cell lymphoma (ALK+ ALCL), which responds well to the cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) regimen [9].