Lymphoma classification update: T-cell lymphomas, Hodgkin lymphomas, and histiocytic/dendritic cell neoplasms

Abstract

Lymphomas are classified based on the normal counterpart, or cell of origin, from which they arise. Because lymphocytes have physiologic immune functions that vary both by lineage and by stage of differentiation, the classification of lymphomas arising from these normal lymphoid populations is complex. Recent genomic data have contributed additional depth to this complexity. Areas covered: Lymphoma classification follows the World Health Organization (WHO) system, which reflects international consensus and is based on pathological, genetic, and clinical factors. The present review focuses on the classification of T-cell lymphomas, Hodgkin lymphomas, and histiocytic and dendritic cell neoplasms, summarizing changes reflected in the 2016 revision to the WHO classification. These changes are critical to hematologists and other clinicians who care for patients with these disorders. Expert commentary: Lymphoma classification is a continually evolving field that needs to be responsive to new clinical, pathological, and molecular understanding of lymphoid neoplasia. Among the entities covered in this review, the 2016 revisions in the WHO classification particularly impact T-cell lymphomas, including a new umbrella category of T-follicular helper cell-derived lymphomas and evolving recognition of indolent T-cell lymphomas and lymphoproliferative disorders.

Keywords: Hodgkin lymphoma; Non-Hodgkin lymphoma; T-cell lymphoproliferative disorder; World Health Organization (WHO); anaplastic large cell lymphoma; angioimmunoblastic T-cell lymphoma; dendritic cell tumors; histiocytic sarcoma; lymphoma classification; peripheral T-cell lymphoma.

Figure 1

Systemic and localized ALK-negative anaplastic large cell lymphomas. (a) Systemic ALK-negative anaplastic large cell lymphoma. H&E stain of a lymph node section shows sheets of neoplastic cells. (b) The tumor cells stain strongly and uniformly for CD30 by immunohistochemistry. (c) Fluorescence in situ hybridization showed this case to have a DUSP22 rearrangement, a finding that has been associated with favorable prognosis. The image shows a single tumor cell nucleus (blue). Hybridization with red and green breakapart probes flanking the DUSP22-IRF4 locus on 6p25.3 show one normal fusion signal (f) and abnormal separation of the red and green signals corresponding to the other allele (arrows), indicating a chromosomal rearrangement. (d) Breast implant-associated anaplastic large cell lymphoma involving the seroma cavity and fibrous capsule surrounding a breast implant. H&E stain shows clusters of cells that have pleomorphic nuclear features (inset; high magnification). Full color available online.

Figure 2

Indolent T-cell lymphoproliferative disorder of the gastrointestinal tract. (a) Low-power H&E image of fragments of mucosa from an endoscopic duodenal biopsy. (b) A higher power H&E image shows an infiltrate of small lymphocytes with bland cytological features (inset). (c) Nearly all the lymphocytes stain for CD4 by immunohistochemistry, and leave the intervening glands (g) relatively unaffected. (d) Staining for CD8 shows only occasional scattered cells. The T cells were shown to be clonal by molecular studies (not shown). This CD4-positive phenotype is less common than a CD8-positive phenotype in this disorder [53].