Erdheim-Chester disease, moving away from the orphan diseases: A case report.

With approximately 750 cases reported, Erdheim-Chester disease is an exceedingly rare histiocyte cell disorder. Affected sites typically include long bones, large vessels and central nervous system. However, cutaneous and pulmonary involvement can also occur. The diagnosis is ascertained by identification of foamy histiocytes positive for CD68, CD163, and factor XIIIa on immunoperoxidase staining. Recently published literature have described an association between Erdheim-Chester disease and BRAF V600E mutation. This finding prompted the investigation of therapeutic possibilities with BRAF inhibitors, successful agents against other BRAF mutation-positive diseases. Vemurafenib, a BRAF kinase inhibitor, has been shown to be effective in BRAF V600E mutation-positive malignancies, such as NSCLC and melanoma, as well as in several case reports of Erdheim-Chester disease. We report a case of Erdheim-Chester disease diagnosed at our institution, treated with vemurafenib.