ALK and anaplastic large cell lymphoma: There are more than 25 unique types of PTCL, and in North America the most common subtypes are Peripheral T-Cell Lymphoma – Not Otherwise Specified (PTCL-NOS) (34%), Angioimmunoblastic T-Cell Lymphoma (AITL) (16%), anaplastic lymphoma kinase (ALK) negative Anaplastic Large Cell Lymphoma (ALCL) (16%), and ALK positive ALCL (8%).