AB Science SA announced that it has received authorization from the French National Agency (ANSM) to resume patient enrollment in the confirmatory Phase 3 study of masitinib (AB15003) in mastocytosis. This authorization follows the validation in July 2021 by the ANSM [1] of the measures proposed by AB Science to reinforce patient safety related to cardiac risk in its ongoing studies. This authorization is the result of a constructive interaction with the French agency based on signal detection, which shows that the pharmacovigilance system in place is properly working. This is the second clinical study for which patient enrollment has been authorized to resume, following the authorization received in amyotrophic lateral sclerosis [2]. AB Science expects to be able to progressively resume global patient enrollment in mastocytosis study during the month of September. This temporary interruption does not mo ify the recruitment schedule, with recruitment completion expected in 2022 for this confirmatory study, as initially planned. As a reminder, study AB15003 is a multicenter, randomized, double blind, placebo-controlled, phase 3 study to compare the efficacy and safety of masitinib dose titration up to 6 mg/kg/day with that of placebo in treatment of patients with severe indolent systemic mastocytosis, unresponsive to optimal symptomatic treatment. The study is designed to enroll 140 patients with or without the D816V mutation of c-Kit. The primary endpoint is a measure of the cumulative response on 3 severe symptoms of mast cell mediator release (pruritus, flush and depression) from week 8 to week 24. This AB15003 study is intended to confirm the previously published results from the first Phase 3 study (AB06006), which demonstrated that masitinib can substantially reduce severe symptoms associated with indolent systemic mastocytosis, regardless of a patient's c-Kit mutational status. In this previous study, the superiority of masitinib was measured by the cumulative 75% response rate until week 24 on the handicaps of pruritus or flushes or depression or fatigue (4H75% response). The 4H75% response was 18.7% for the masitinib treatment-arm versus 7.4% for the placebo treatment-arm. Study results were published in The Lancet.