Background and Importance Rosai Dorfman disease (DRD) is a rare non-Langerhans histiocytosis. There is no established treatment, and if necessary there are few therapeutic options which have limited evidence. DRD has recently been related to the identification of mutations in the mitogenic activation protein kinase (MAPK)-dependent signaling pathway, being an interesting target for its treatment.

Aim and Objectives This report will discuss the case of a patient with DRD who responded adequately to targeted therapy with trametinib, after failure to several lines of treatment.

Material and Methods The episodes in oncohematology day hospital of patients diagnosed in a tertiary University Hospital are reviewed. A bibliographic review of cases described with similar symptoms was carried out. The Pharmacy Service collaborated in the search for a possible effective treatment and justified the need to start treatment with a MEK inhibitor.

Results 45-year-old patient being followed up for gastrointestinal episodes and lymphadenopathy who was diagnosed with histiocytosis compatible with DRD in 2021.It was started treatment with corticosteroids at a dose of 1 mg/kg, which in the event of refractoriness was changed to peginterferon alfa (90 mcg) without response. At the beginning of March 2023, he was admitted to the ward due to deep vein thrombosis and pulmonary thromboembolism. He received a new treatment regimen with anakinra for 13 days without success. The case is consulted and it is decided to change to a MEK inhibitor. Its use is requested outside of indication despite not obtaining any alteration in the MAPK pathway. Trametinib was started at a dose of 1 mg/day. After 3 months, she currently has good tolerance with platelet counts of 37,000 and decreased lymphadenopathy. As toxicity to trametinib, acneiform rash have been reported.

Conclusion and Relevance There is no well-defined protocol for the treatment of DRD and therefore they represent a diagnostic and therapeutic challenge. This case contributes to the limited data published on targeted therapy with MEK inhibitors in DRD when cases are refractory to traditional therapies.

References and/or Acknowledgements 1. Successful Treatment of Non-Langerhans Cell Histiocytosis with the MEK Inhibitor Trametinib:A Multicenter Analysis. Blood Advances. 2022, Dr. Diamond.

2. Multiple Drug Regimen-Refractory Rosai-Dorfman-Destombes Disease Mimicking Relapsing Polychondritis Successfully Treated with Cobimetinib. European Journal of Case Reports in Internal Medicine, 2022.

Conflict of Interest No conflict of interest.