On November 6th, 2017, the U.S. Food and Drug Administration (FDA) approved the drug Zelboraf (vemurafenib), for the treatment of Erdheim-Chester Disease (ECD)[1]. The FDA approved Zelboraf under Priority Review, Breakthrough Therapy, and Orphan Drug designations for the ECD indication. These designations allow the drug accelerated approval and provide incentives to assist and encourage pharmaceutical development in rare diseases.

ECD is a rare form of cancer often affecting adults in their mid-50s. ECD is characterized by excessive production of hitiocytes (white blood cells) that accumulate in tissues and organs. Among ECD patients, approximately 54% have a common B-RAF V600 mutation. B-RAF is a member of the RAF kinase family, which is involved in signal transduction.

Zelboraf, is a B-RAF enzyme inhibitor originally developed to treat melanomas by Plexxikon under the name vermurafenib (PLX4032)[2]. Through a co-development deal with Hoffmann-La Roche it would eventually be marketed as Zelboraf[3]. In clinical studies submitted to the FDA, the targeted treatment with Zelboraf of patients with a B-RAF V600 mutation resulted in approximately half of all patients experiencing a decrease in disease progression and one patient experiencing a reduction in tumor size[4].