[Molecular targeted therapy for Erdheim-Chester disease]

Erdheim-Chester disease (ECD) is a rare form of non-Langerhans histiocytic disease with no established therapeutic approach. Here we report a case of ECD treated with molecular targeted therapy. A 61-year-old woman diagnosed with ECD with BRAF^V600E mutation received combination therapy with a BRAF inhibitor (dabrafenib) and MEK inhibitor (trametinib). Grade 1 fever and liver injury were detected early in the course of treatment, leading to temporary interruption. However, treatment was successfully resumed with concomitant administration of prednisolone. The BRAF^V600E allele frequency in plasma cell-free DNA became negative at 8 weeks of treatment, and PET/CT confirmed a partial metabolic response at 24 weeks. Recent studies have demonstrated the benefit of molecular targeted therapy for ECD. However, due to the rarity of ECD, treatment guidelines remain poorly defined, with limited guidance on indicators of treatment efficacy, optimal treatment duration, and criteria for treatment cessation. In the case of our patient as well, it will be necessary to consider the duration of treatment while carefully monitoring the clinical course.