In September 2018, the World Health Organization (WHO) and European Organization for Research and Treatment of Cancer (EORTC) released an updated version of their 2005 classification for primary cutaneous lymphomas. The main changes in the updated classification were summarized in a review recently published in Blood.

The authors recognized 3 new lymphoproliferative disorder (LPD) subtypes and recategorized primary cutaneous CD4+ small/medium T-cell lymphoma as a LPD. New sections were added for 2 kinds of cutaneous T-cell lymphoma (CTCL): chronic active Epstein-Barr virus (EBV)-positive LPD in childhood and primary cutaneous acral CD8+ T-cell lymphoma.

EBV-positive disorders typically manifest with a papulovesicular eruption on areas of skin that have been exposed to the sun, or with ulceronecrotic lesions at the site of a mosquito bite. These disorders have a variable clinical course, as skin lesions may recur for many years before progression to systemic lymphoma.

Primary cutaneous CD8+ T-cell lymphoma is characterized by a diffuse infiltrate of CD3+, CD4-, CD8+, and CD30- cytotoxic T cells. Despite this aggressive histology, however, these lesions have an indolent clinical behavior, and the prognosis for patients with this kind of CTCL is excellent.

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Primary cutaneous marginal zone lymphoma (PCMZL), which was previously categorized as a type of cutaneous B-cell lymphoma (CBCL), was recategorized as a type of marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma). PCMZL was noted as having an indolent clinical course and a 5-year disease-specific survival rate near 100%. Recent evidence points towards the existence of 2 types of PCMZL: cases where CXCR3 is expressed and cases where it is not. The similarities between PCMZL, MALT lymphomas, and pseudo-B-cell lymphomas led the authors to suggest that B-cell proliferations may exist as a continuous spectrum.

EBV-positive mucocutaneous ulcer was also recognized as a B-cell LPD. Conversely, primary cutaneous diffuse large B-cell lymphoma was removed as a classification category.

In addition, the authors summarized recent research regarding the molecular mechanisms underlying lymphoma pathogenesis. They reported that loss of CDKN2A and the presence of MYD88 L265 mutations were both associated with inferior prognosis of primary cutaneous large B-cell lymphoma but not of primary cutaneous follicle center lymphoma.

The authors concluded, “While genetic markers may become increasingly important, integration of histologic, immunophenotypic, genetic, and clinical data remains essential for an accurate diagnosis.”

Disclosure: One of the authors declares an affiliation with the pharmaceutical industry. Please refer to the original study for a full list of disclosures.

Reference

1. Willemze R, Cerroni L, Kempf W, et al. The 2018 update of the WHO-EORTC classification for primary cutaneous lymphomas [published online January 11, 2019]. Blood. doi: 10.118/blood-2018-11-881268