Recent epidemiology studies have identified a steady increase in the incidence of cutaneous lymphomas over the past few decades. Although possible explanations for this increased incidence include heightened awareness of these conditions as well as a more refined diagnostic acuity by dermatologists and pathologists, an increase secondary to environmental factors cannot be discounted. Our understanding of cutaneous lymphomas keeps evolving. Consequently, our knowledge and understanding of cutaneous lymphomas requires reconsideration of past dogma and critical revision of the new proposals. In this article, some hot topics and important new findings in the field are reviewed.
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The World Health Organization-European Organization for Research and Treatment of Cancer classification of cutaneous lymphomas is the result of a consensus among dermatologists, dermatopathologists, and hematopathologists and reflects the unique characteristics of skin lymphomas.
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Subcutaneous panniculitis-like T-cell lymphoma is often preceded by a nondiagnostic lymphoid infiltrate of the subcutaneous fat, which may share features with lupus profundus.
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Marginal zone lymphoma is an indolent condition, which can present with a marked plasmacytic differentiation. These cases need to be differentiated from plasmacytomas, which are often associated with multiple myeloma.
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Cutaneous γδ lymphomas can present with a variety of pathologic patterns, ranging from a lichenoid superficial pattern to a deep necrotizing panniculitic process.
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Follicular T-helper cells may be the cell of origin to certain skin lymphomas, including d’emblée presentation of MF and small/medium pleomorphic T-cell lymphomas.
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There is some clinical and pathologic overlap between pediatric lymphomatoid papulosis and pityriasis lichenoides acuta, especially when the infiltrate is primarily CD8 positive.
Our understanding of cutaneous lymphomas keeps evolving, as shown by the marked increase of scientific literature in all areas related to cutaneous lymphomas. Consequently, our present knowledge and understanding of cutaneous lymphomas requires reconsideration of past dogma and critical revision of the new proposals. In this article, some hot topics and important new findings in the field are reviewed.
European Organization for Research and Treatment of Cancer/World Health Organization classification of cutaneous lymphomas: a work in progress
The classification of cutaneous lymphomas has evolved and become more complex over the years, reflecting the contemporary understanding of these conditions. This trend will most certainly continue in the future as we continue to gain knowledge of the field. The current classification, established in 2005, is based on a consensus of the European Organization for Research and Treatment of Cancer (EORTC) and World Health Organization (WHO) as the result of a remarkable effort to find common ground between European dermatologists and American hematopathologists. The essence of this classification was incorporated in the most recent lymphoma classification update from WHO in 2008 ( Tables 1 and 2 ). For the first time, distinct cutaneous entities that in the past would had been diagnosed and classified differently depending on specialty and location of the physician are now broadly recognized by the scientific community as specific entities. This consensus was the result of an unprecedented meeting of minds at which extensive discussions took place between hematopathologists, dermatologists, and dermatopathologists. On reviewing their extensive experiences and taking into consideration morphologic, immunophenotypical, and molecular evidence, the experts assigned distinct skin lymphoma entities based on the unique characteristics of skin lymphomas even as compared with the same morphologic conditions in primary lymphoid organs. For instance, primary cutaneous follicle center cell lymphoma, unlike the nodal counterpart, lacks the typical t(11;14) translocation and diffuse large B-cell lymphoma, leg-type (DLBL-LT) became the first skin lymphoma to incorporate an anatomic site in the name. However, this new lymphoma subtype, as is discussed later, is still a debatable entity for some experts. Finally, we can use a cutaneous lymphoma classification that makes sense to the clinical dermatologists from a prognostic point of view and is accepted by the pathology community. Although the WHO-EORTC classification of cutaneous lymphomas represents a major advancement over previous classifications, several issues remain unsolved. There are provisional entities like primary cutaneous aggressive epidermotropic CD8+ T-cell lymphoma (often referred to as Berti lymphoma), which as we learn more about these rare conditions, should eventually become a definitive entity. There are other entities like CD4+ small to medium-sized pleomorphic T-cell lymphoma (CD4+SMPTCL) and probably lymphomatoid papulosis that in our opinion may be overdiagnosed because reactive conditions can mimic these conditions and also because the defining criteria as described in the consensus publications are imprecise and prone to misinterpretation. SMPTCL is diagnosed at our center to comply with classification standards. However, we believe that they should be diagnosed as a cutaneous lymphoid hyperplasia or pseudolymphoma. Most if not all patients presenting with unilesional CD4+SMPTCL have an entirely indolent course, regardless of the presence or absence of T-cell clonality. This indolent course has been confirmed by a large cohort from the Graz group that suggested an undeterminate significance, although none of their patients showed tumor progression. Cetinozman and colleagues have also reported that the lesions currently diagnosed as CD4+SMPTCL express a follicular T-helper phenotype that is identical to lesions reported as pseudolymphoma in the past. Lymphomatoid papulosis as a subtype of CD30 lymphoproliferative disorder also remains poorly defined, and as a consequence, patients with brief papular episodes of unclear nature but focal CD30 expression may be misdiagnosed as suffering from a lymphoproliferative disorder. To further complicate this entity, patients may be diagnosed with the so-called lymphomatoid papulosis type B with complete absence of CD30 expression. The classification of cutaneous lymphomas also includes conditions that are often systemic from their onset, like adult T-cell leukemia/lymphoma or extranodal natural killer (NK)/T-cell lymphoma.
| Mature T-Cell and NK Cell Neoplasms | Cutaneous Involvement |
|---|---|
| T-cell prolymphocytic leukemia | Rare |
| T-cell large granular lymphocytic leukemia | Rare |
| Chronic lymphoproliferative disorder of NK-cells a | Rare |
| Aggressive NK cell leukemia | Rare |
| Systemic EBV T-cell lymphoproliferative disease of childhood | Rare |
| Hydroa vacciniforme-like lymphoma | Yes |
| Adult T-cell leukemia/lymphoma | Yes |
| Extranodal NK/T-cell lymphoma, nasal type | Common |
| Enteropathy-associated T-cell lymphoma | Rare |
| Hepatosplenic T-cell lymphoma | No |
| Subcutaneous panniculitis-like T-cell lymphoma | Yes |
| Mycosis fungoides | Yes |
| Sézary syndrome | Yes |
| Primary cutaneous CD30+ T-cell lymphoproliferative disorder (LyP and PCALCL) | Yes |
| PC aggressive epidermotropic CD8+ cytotoxic T-cell lymphoma a | Yes |
| PC γδ T-cell lymphoma | Yes |
| PC small to medium-size CD4+ T-cell lymphoma a | Yes |
| Angioimmunoblastic T-cell lymphoma | Rare |
| ALK+ | Rare |
| ALK− a | Common |
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