[Erdheim-Chester disease].

Erdheim-Chester disease is a rare and orphan disease. Despite having been overlooked previously, numerous new cases have been diagnosed more recently. The number of Erdheim-Chester disease cases reported has increased substantially: more than 300 new cases have been published in the past 10 years. This situation is mainly a result of the generally better awareness among pathologists, radiologists, and clinicians of various aspects of this rare disease. The field has been particularly active in the last few years, with evidence of the efficacy of interferon-α, the description of a systemic pro-inflammatory cytokine signature, and most recently, reports of the dramatic efficacy of BRAF inhibition in severe, BRAF(V600E) mutation-associated cases of Erdheim-Chester disease. Also, BRAF mutations have been found in more than half of the patients with Erdheim-Chester disease who were tested. Detailed elucidation of the pathogenesis of the disease is likely to lead to the development of better targeted and more effective therapies.