Primary Cutaneous Peripheral T-Cell Lymphoma NOS: Diagnostic Criteria and Challenges.

Primary cutaneous peripheral T-cell lymphoma not otherwise specified (PTCL NOS) denotes lymphomas that do not conform to a recognized entity. Within this category, 3 specific lymphoproliferative diseases had been granted provisional status pending further confirmation of their validity as distinct entities; acral CD8+ lymphoma-recently accepted as acral CD8+ lymphoproliferative disorder-aggressive epidermotropic CD8+ cytotoxic T-cell lymphoma, and CD4+ small-medium T-cell lymphoproliferative disorder. The adoption of stringent diagnostic criteria, which include clinical, morphological, and immunohistochemical data, and some inherent variations of these within individual cases, raises problems as to the boundaries between these tumors and a diagnosis of PTCL NOS. This review discusses the evolution of our knowledge of these tumors and their diagnostic criteria with respect to the wider PTCL NOS category.