Cutaneous peripheral T-cell lymphomas, unspecified/NOS and rare subtypes: a heterogeneous group of challenging cutaneous lymphomas.

Cutaneous peripheral T-cell lymphoma, unspecified/not otherwise specified (PTL NOS) represents a phenotypically and prognostically heterogenous group of cutaneous T-cell lymphomas (CTCL) that do not fit into any of well defined defined CTCL subtypes. In the WHO-EORTC classification as well as the WHO classification, three entities have been delineated as provisional rare subtypes of PTL based on their characteristic clinico-pathological, immunophenotypic and prognostic features and have been separated out from PTL, NOS: Primary cutaneous CD4-positive small/medium T-cell lymphoma (CD4+ SMTL), primary cutaneous CD8-positive aggressive epidermotropic T-cell lymphoma (CD8+ AECTCL), and primary cutaneous gamma/delta T-cell lymphoma (CGD-TCL). CD4+ SMTL manifests in most patients with a solitary nodule in the head and neck area and nodular infiltrates of CD4+ small to medium-sized lymphocytes with nuclear pleomorphism. The prognosis of this lymphoproliferation is excellent in patients with a solitary lesion, but may be impaired in patients with multifocal disease. Rapidly evolving erosive or necrotic plaques and nodules with an epidermotropic infiltrate of CD8+ atypical lymphocytes are the hallmark of CD8+ AECTCL, which exhibits a poor prognosis. CGD-TCL displays a broad spectrum of clinical and histological manifestations with expression of the T-cell receptor gamma/delta chain as the common denominator and diagnostic marker. As most of other forms of PTL, CGD-TCL carries a poor prognosis. Despite the rarity of PTL NOS, clinicians as well as dermatopathologists and pathologists should be familiar with these rare CTC, especially since most of these lymphomas exhibit an unfavourable prognosis. Immediate intense treatment with multiagent chemotherapy and hematopoietic stem cell transplantation is indicated in patients with PTL NOS. This review focuses on the clinicopathological aspects, the diagnostic criteria and the classification of the rare subtypes of PTL and PTL NOS.