An occurrence of eosinophilic folliculitis and alopecia associated with a sustained complete response to mogamulizumab in Sézary syndrome: a case report.

Mogamulizumab is a monoclonal antibody that binds to C-C chemokine receptor 4 (CCR4), initiating antibody-dependent cellular cytotoxicity. CCR4 is highly expressed in the cutaneous T-cell lymphoma subtypes mycosis fungoides and Sézary syndrome (SS), and mogamulizumab has been shown to be effective in patients with these conditions who were refractory to at least one prior systemic treatment. One of the more common adverse events encountered with mogamulizumab is rash, which may mimic disease progression and lead to premature discontinuation. Moreover, there has been some evidence to suggest that mogamulizumab-associated rash (MAR) is associated with improved outcomes in some patients, particularly those with SS. This report presents the case of a 72-year-old woman with SS, which manifested with macular and papular lesions and abnormal blood cytometry, who was treated with mogamulizumab after failure of bexarotene and photopheresis combination therapy. She achieved a complete response (CR), but experienced lymphopenia associated with histologically proven eosinophilic folliculitis (EF) of the scalp and alopecia. The EF responded well to initial topical corticosteroids, defined by regression of erythema and pustular involvement and reduction in pruritus-like symptoms, but without hair regrowth. Mogamulizumab was withdrawn after 32 cycles, but CR was maintained. To date, EF persists in the form of diffuse erythema without pustules or pruritus. A link between cluster of differentiation 4 lymphopenia and EF has previously been established; therefore, EF should be considered in patients who develop rash and lymphopenia while receiving treatment with mogamulizumab. MAR has been associated with clinical response to mogamulizumab, and this case report adds to the evidence that EF may also be associated with sustained clinical response following treatment cessation. However, regular monitoring is required to prevent a relapse of SS. Prospective studies are needed to confirm whether such an association between EF and CR following mogamulizumab exists.