Mogamulizumab-associated rash - Case series and review of the literature.

Mogamulizumab, a monoclonal antibody directed against CC chemokine receptor 4, is approved as a second-line treatment of mycosis fungoides and Sézary syndrome. One of the most common side effects is mogamulizumab-associated rash (MAR), which can present in a variety of clinical and histological types. Clinically, it can be difficult to differentiate between MAR and progression of the underlying disease, so histological examination is crucial for clinicopathological correlation. Current data analyses suggest that MAR is more common in patients with Sézary syndrome and is associated with a significantly better response to treatment, making the distinction from disease progression particularly important. The management of MAR depends on its severity, and therapy may need to be paused. This article presents three cases from our clinic and reviews the current literature on MAR. It emphasizes the importance of understanding MAR in the management of patients with cutaneous lymphomas.

Utility of T-cell immunosequencing in distinguishing mycosis fungoides progression from treatment related cutaneous adverse events.

Cutaneous adverse events of both topical and systemic drugs in patients with mycosis fungoides (MF) present a diagnostic challenge as it is often difficult to distinguish drug associated rash from disease progression in the skin. Mogamulizumab and mechlorethamine gel are approved treatments for MF, both of which can cause treatment related cutaneous adverse events. It can often be challenging to distinguish mogamulizumab associated rash (MAR) and mechlorethamine gel associated hypersensitivity dermatitis from MF progression both clinically and histologically. High-throughput sequencing (HTS) of the T-cell receptor (TCR), also known as immunosequencing, can be used to assess T-cell clonality to support a diagnosis of MF. After identification of the malignant TCR clone at baseline, immunosequencing can track the established malignant TCR sequence and its frequency over time with high sensitivity. As a result, immunosequencing clone tracking can aid in distinguishing disease progression from treatment side effects. Here, we present a case series to demonstrate how monitoring of the malignant T-cell frequency by immunosequencing can aid in diagnosis of mogamulizumab and mechlorethamine gel cutaneous adverse events.