Mycosis fungoides/Sézary syndrome and systemic Janus kinase inhibitors: a real-world retrospective study on behalf of the EORTC CLTG

Janus kinase inhibitors (JAKis) are increasingly used in patients with mycosis fungoides (MF)/Sézary syndrome (SS), often outside of intentional lymphoma-directed treatment, yet their real-world impact remains uncertain and poorly characterized. Our multicentre experience suggests that disease acceleration may occur in specific clinical contexts, particularly in patients initially diagnosed with dermatitis who were later recognized as having MF/SS while receiving JAKis. It remains uncertain whether this acceleration represents a direct drug-related effect. Observations in post-transplant settings warrant further investigation, particularly given ruxolitinib’s role in this context. However, symptom-focused benefit may be observed in carefully selected patients. Collectively, these findings highlight that the use of JAKis in treating patients with MF/SS should be undertaken with caution.