Neoplastic nodular T-cell pattern: An approach to diagnosis of neoplastic nodular T-cell lymphomas of the skin

We describe a group of peripheral T-cell lymphoma (PTCL) with high predilection to the skin that presents in a dermotrophic nodular pattern. These diseases include the rare group of cutaneous PTCLs other than mycosis fungoides (MF), as well as transformed MF. The putative biologic origin, immunologic, and gene expression profile for the group are discussed. For individual entities, the definition, epidemiology, clinical appearance, pattern of infiltration, cytomorphology, immunophenotype, cytogenetics, molecular findings, clinical behavior, and differential diagnosis are included, highlighted with summary tables and histopathologic images. Although cutaneous lymphomas are histologically similar to nodal systemic lymphomas, the former have a different course, require localized and stage-specific management, and should be recognized as separate entities. This chapter focuses on the primary cutaneous T/NK-cell lymphomas, which represent about 32 % of primary cutaneous T-cell subtypes. We include peripheral T-cell lymphoma, unspecified, transformed MF, solitary CD4 + pleomorphic T-cell lymphoma (primary cutaneous small-medium-sized T cell lymphoma), cutaneous gamma-delta T-cell lymphoma, angioimmunoblastic T-cell lymphoma, extranodal NK/T-cell nasal type, cutaneous HTLV-1 adult T-cell leukemia/lymphoma (ATLL), as well as their differential diagnosis. Nodular forms of cutaneous CD30-positive lymphomas, although part of this group, are separated into another chapter.