New Molecular and Biological Markers in Cutaneous T Cell Lymphoma: Therapeutic Implications.

Purpose of review: Cutaneous T cell lymphomas (CTCLs) exhibit a wide variety of clinical features, histologic characteristics, and genetic drivers. We review novel molecular findings that inform our understanding of the pathogenesis of CTCL, with a focus on the tumor microenvironment (TME).

Recent findings: There is increasing evidence challenging the model of T_CM:mycosis fungoides (MF) and T_EM:Sézary syndrome (SS) phenotype. Phylogenetic analysis performed using whole-exome sequencing (WES) raises the possibility that MF can arise without a common ancestral T cell clone. The detection of ultraviolet (UV) marker signature 7 mutations in the blood of patients with SS raises questions about the role of UV exposure in CTCL pathogenesis. There is also increasing interest on the role of the TME in CTCL. Existing therapies such as the RXR retinoid bexarotene and the anti-CCR4 monoclonal antibody mogamulizumab may act through the CTCL TME by impacting the CCL22:CCR4 axis, while cancer-associated fibroblasts (CAFs) in the CTCL TME contribute to drug resistance, as well as a Th2 milieu and tumor growth via secretion of pro-tumorigenic cytokines. Staphylococcus aureus (SA) is a frequent cause of morbidity among CTCL patients. SA may positively select for malignant T cells through adaptive downregulation of alpha-toxin surface receptors and promotion of tumor growth via upregulation of the JAK/STAT pathway. Recent molecular advancements have contributed to our understanding of the pathogenesis of CTCL and shed light into the potential mechanisms of existing therapies. Further understanding of the CTCL TME may fuel the discovery of novel therapies for CTCL.