A case report of refractory advanced-stage mycosis fungoides: successful treatment and improved patient quality of life with mogamulizumab.

Mycosis fungoides (MF), the most common form of cutaneous T-cell lymphoma, is characterized by patches, plaques, and, in advanced stages, tumors and erythroderma. Early-stage MF may progress to advanced-stage disease in up to one-third of patients, conferring a worse prognosis and typically requiring systemic treatment for extracutaneous involvement. The most frequently reported signs and symptoms are pain, pruritus, scaling, and skin redness, with pruritus, the most bothersome symptom, exerting a profound impact on patients' health-related quality of life (HRQoL). These dermatologic signs and symptoms can overlap with those of other benign inflammatory dermatoses, such as eczema and psoriasis, and therefore, diagnostic delay is common in patients with MF. Moreover, identifying patients with features adversely affecting prognosis (e.g. large-cell transformation or folliculotropic variant) is a significant challenge. We report the case of a 75-year-old female patient who was misdiagnosed with eczema and then pityriasis rubra pilaris and consequently did not receive treatment for MF for 4 years. The patient was eventually correctly diagnosed with MF [stage IIIB (T4 N1 M0 B1)] in September 2018. The patient received several systemic treatments; however, she did not respond to or tolerate the treatments. Due to lack of treatment response, in July 2021, she was initiated on mogamulizumab, an anti-CC chemokine receptor 4 antibody with demonstrated effectiveness and licensed approval for adults with MF/Sézary syndrome who have received one or more prior systemic therapies. Treatment rapidly led to a complete response in blood after 1 week and in skin after 4 months. Mogamulizumab was well tolerated by the patient, who also reported a significant improvement in her HRQoL. After 1 year in complete response, mogamulizumab was discontinued. This case highlights the need for accurate and early diagnosis of MF to initiate disease-specific treatment and the importance of considering patient HRQoL when treating this condition.