Immune-related adverse events with mogamulizumab in cutaneous T-cell lymphoma: A multicentre study

Mogamulizumab, an anti-CCR4 monoclonal antibody used in advanced mycosis fungoides (MF) and Sezary syndrome (SS), also depletes regulatory T cells, potentially leading to immune-related adverse events (irAEs). Unlike mogamulizumab-associated rash (MAR), other irAEs remain poorly documented to date.

To estimate the prevalence of mogamulizumab-associated irAEs (excluding MAR), characterize their clinical profile and assess management strategies and outcome.

A retrospective nationwide multicentre survey was conducted using the French Study Group on Cutaneous Lymphomas (GFELC) database with standardized questionnaires collecting demographic, clinical and therapeutic data. An exploratory pharmacovigilance analysis was also performed using the WHO pharmacovigilance database, VigiBase.

Among 403 treated patients from 19 participating centres, 34 patients (8.4%) experienced at least one irAE (41 events overall, event rate 10.2%). The most frequent irAEs involved the endocrine system, skin, and liver. Severe (grade ≥3) or serious irAEs occurred in about one-third of cases, resulting in permanent treatment discontinuation in 29%. Most events occurred after several months of treatment, often in patients experiencing objective responses. In VigiBase (2464 reports), reported irAEs were most frequently digestive, musculoskeletal, cutaneous, and hepatic.

In this large retrospective series, a minority of patients developed irAEs during mogamulizumab treatment, although a substantial proportion were rated as severe and led to permanent treatment discontinuation. These findings highlight the need for systematic detection, as with immune checkpoint inhibitors, early recognition and prolonged monitoring, as irAEs may occur late during treatment. Prospective studies are warranted to refine epidemiological data along with diagnostic and therapeutic strategies.