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INTRODUCTION

Primary cutaneous lymphomas are a heterogeneous group of extranodal non-Hodgkin lymphomas arising from malignant clonal transformation of skin homing or/and skin resident T cells or B lymphocytes and hematodermic precursor neoplasias (plasmacytoid dendritic cell neoplasias). Cutaneous lymphomas (Fig. 119-1) are defined as a heterogeneous group with distinct variability in clinical presentation, histopathology, immunophenotyping, and prognosis.

Figure 119-1

Cutaneous lymphomas. ENMZL, extranodal marginal zone lymphoma; PCFCL, primary cutaneous follicle center lymphoma; PCLBCL, primary cutaneous diffuse large B-cell lymphoma; PCMZL, primary cutaneous marginal zone lymphoma.

Primary cutaneous lymphomas are defined entities with a completely different clinical behavior and prognosis as nodal non-Hodgkin lymphomas and require different treatment approaches.

For this reason the European Organization for Research and Treatment of Cancer (EORTC) and World Health Organization (WHO) published a consensus classification for cutaneous lymphomas in 2005.1 This first common classification (WHO-EORTC) categorizes the entities according to lineage and then according to a combination of morphology, immunophenotype, genetic features, and clinical syndromes, and constitutes the basis for the classification of cutaneous lymphomas in the WHO classification 2008 and the revised classification of lymphoid neoplasias in 2016.2,3 This chapter discusses the most frequent cutaneous T-cell lymphomas (CTCLs)—mycosis fungoides (MF), Sézary syndrome, primary cutaneous anaplastic large-cell lymphoma, and lymphomatoid papulosis—and the most frequent cutaneous B-cell lymphomas (CBCLs)—primary cutaneous follicle center lymphoma (PCFCL), primary cutaneous marginal zone lymphoma (PCMZL), and primary cutaneous diffuse large B-cell lymphoma (PCLBCL), leg type. These 7 types of cutaneous lymphoma represent nearly 90% of all cutaneous lymphomas. Rare entities occurring primary in the skin are also described.

EPIDEMIOLOGY

CTCLs represent the second most common group of extranodal lymphomas after the primary GI lymphomas. The incidence of CTCLs has been increasing and is currently, in the United States, estimated to be 6.4 cases/million people between 1993 and 2002 or 7.7 cases/million people between 2001 and 2005. The incidence of CTCL increases significantly with age, with a median age at diagnosis in the mid-50s and a fourfold increase in incidence appreciated in patients older than age 70 years.4-6

PRIMARY CUTANEOUS T-CELL LYMPHOMAS

CTCLs are non-Hodgkin lymphomas characterized by clonal expansion of activated T-cells expressing the E-selectin ligand cutaneous lymphocyte antigen and chemokine receptors (eg, CCR4, CCR8, CCR10) that are required for their subsequent trafficking to the skin.7-9 Clonal expansion is followed by differentiation into multiple subsets of effector and memory cells. Human skin is protected by 4 functionally-distinct populations of T cells, 2 resident and 2 recirculating, with differing territories of migration and distinct functional activities. Central memory cells (TCM) retain the ability to access the peripheral blood and lymph nodes. Effector memory cells (TEM), in contrast, migrate into extranodal sites, including the skin, where a subset will remain ...

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