Cutaneous Lymphoma Molecular Pathogenesis, Diagnosis and Management

Dear Colleagues,

Primary cutaneous lymphomas are classified based on the type of malignant cells driving the disease process: primary cutaneous B-cell lymphomas (PCBCLs) or primary cutaneous T-cell lymphomas (CTCL). CTCLs are a heterogeneous group of lymphoid malignancies derived from skin-homing T-cells. CTCLs account for 75% of all cutaneous lymphomas. While, Mycosis fungoides (MF), primary cutaneous Anaplastic Large Cell Lymphoma (and other CD30+ lymphoproliferative malignancies), and Sézary Syndrome represent the commonly recognized forms of the disease, other variants as defined by the WHO-EORTC classification are becoming increasingly prevalent (e.g., primary cutaneous CD4+ small/medium T-cell lymphoproliferative disorder and others). CTCL can be difficult to diagnose as it often mimics other dermatoses such as chronic eczema, psoriasis, drug eruptions, or skin infections. Skin biopsy and the detection of T-cell receptor (TCR) clonality are often not diagnostic for this malignancy. As a result, it takes on average ~6 years to establish the diagnosis of CTCL. Currently, there are no validated molecular markers to help identify this cancer and shorten the time to diagnosis. Furthermore, while >70% of patients present with stage I disease, only 20%–30% of them progress to higher stages. Currently, it is difficult to predict which patients will progress and which ones will experience an indolent disease course. Despite the available new treatments, the survival of patients with advanced CTCL remains poor (2–4 years).

PCBCL is a group of extranodal B-cell non-Hodgkin lymphomas that involve the skin. They account for approximately 25% of all cutaneous lymphomas and are classified as primary cutaneous marginal zone lymphoma (PCMZL), primary cutaneous follicle-center cell lymphoma (PCFCL), and diffuse large B-cell lymphoma, leg type (PCDLBCL, LT). Recently, Epstein–Barr virus positive (EBV+) mucocutaneous ulcer (EB-MCU) was added as a new provisional distinct entity. PCBCLs conventionally present as violaceous plaques, or nodules. Diagnosis requires skin biopsy and histological examination with appropriate immunohistochemical staining.

While certain external triggers/promoters (e.g., Borrelia burgdorferi for PCMZL, S. Aureus for CTCL or Human T-Cell Lymphotropic virus (HTLV-1) for Adult T-Cell Leukemia/Lymphoma) have been identified or suspected, the pathogenesis of both PCBCL and CTCL remains elusive. The field lacks reliable diagnostic markers for CTCL, or prognostic markers for both CTCL and PCBCL as well as novel therapeutic targets.

This Topical Collection is dedicated to research that can enhance our understanding of the molecular pathogenesis and evolution of cutaneous lymphomas, the genetics/genomic components of the disease, the diagnostic/prognostic markers, the role of the microbiome, as well as novel avenues for treating these challenging diseases.

Dr. Ivan V. Litvinov
Dr. Robert Gniadecki
Dr. Niels Ødum
Dr. Madeleine Duvic
Dr. Oleg Akilov
Collection Editors

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