AB Science SA announced that it has been authorized by the French Medicine Agency, ANSM, to initiate a Phase II study (AB20006) in patients with severe mast cell activation syndrome. Study AB20006 has also been approved by the U.S. Food and Drug Administration (FDA). MCAS is a disease caused by inappropriate activation of mast cells, which can lead to mast cell mediator release symptoms with a severity ranging from mild to life-threatening.

In this aspect, MCAS is similar to indolent and smoldering systemic mastocytosis (ISM/SSM), however, important differences exist that make MCAS a distinct entity from systemic mastocytosis. In mastocytosis, well-defined mutations result in an aberrant population of mast cells with a marked increased proliferation in tissues, whereas MCAS is driven by greater (ill-defined) mutational heterogeneity that is associated with aberrant mast cell activation but only modest increases in mast cell numbers due to reduced apoptosis. Another striking difference between systemic mastocytosis and MCAS is the prevalence of these diseases.

Systemic mastocytosis is considered to be a rare, orphan disease affecting about 1/100,000 people, whereas MCAS has an estimated prevalence of 1–17% of the population (i.e., at least a 1000-fold difference). Because masitinib has been designed to be a potent inhibitor of mast cell activation (through its action against wild-type c-Kit, Lyn and Fyn tyrosine kinases), it is uniquely well-suited for the treatment of severe MCAS, unlike other c-Kit tyrosine kinase inhibitors that typically target specific c-Kit mutations that are associated with systemic mastocytosis. There are currently no approved therapies for severe MCAS or drugs in clinical development for this indication.