US regulators have approved Roche’s Zelboraf (vemurafenib) for patients with a rare blood condition called Erdheim-Chester disease (ECD) carrying a mutation called BRAF V600.

ECD is a serious blood disease characterised by the abnormal multiplication of certain white blood cells called histiocytes, which can invade normal tissues and organs in the body.

The exact prevalence and incidence of the condition are difficult to determine ast the diseases is so rare, but Roche says that, based on the available data, it’s thought that there are fewer than 500 cases in the US. What is known is that more than 50 percent of people with ECD have BRAF V600 mutation-positive disease.

Zelboraf (vemurafenib) is designed to inhibit some mutated forms of BRAF, which cause abnormal signaling inside cancer cells leading to tumor growth.

The drug was first approved in 2011 for the treatment of patients with inoperable or metastatic melanoma with BRAF V600 mutations.

Its expansion to include the treatment of patients with ECD is based on data from the Phase II VE-BASKET study, which showed an overall response rate of 54.5 percent.

According to Roche, basket studies use an innovative clinical trial design that helps collect data faster by matching a disease’s underlying genetic profile to the mechanism of action of the medicine, as opposed enrolling people based on their disease or its location.

“This FDA decision means people living with Erdheim-Chester disease will now, for the first time, have an FDA-approved treatment option,” said Sandra Horning, MD, Roche’s chief medical officer and head of Global Product Development.

“We are committed to finding new ways to bring medicines to patients with high unmet need, and we are pleased that this innovative clinical trial helped identify Zelboraf for treatment of this rare disease.”