Azacitidine

PRESS RELEASE AB SCIENCE PROVIDES AN UPDATE ON ITS CLINICAL PROGRAM, SUSPENDING SOME NON-PRIORITY CLINICAL TRIALS TO FOCUS ON TWO CLINICAL PROGRAMS Paris, July 10, 2026, 6pm CET AB Science SA (Euronext - FR0010557264 - AB) today provides an update on its clinical development program and announces the discontinuation of certain non-priority clinical studies in order to focus on two clinical programs, the AB8939 program for acute myeloid leukemia and the masitinib program for amyotrophic lateral sclerosis. Following the company’s press release dated April 16 [1], three clinical studies—which the company currently considers non-priority and for which patient enrollment had been suspended—are being discontinued, namely: Phase 2 study (AB20006) of masitinib in mast cell activation syndrome Phase 3 study (AB15003) of masitinib in mastocytosis Phase 3 study (AB20009) of masitinib in progressive forms of multiple sclerosis The discontinuation of these studies is not related to any safety concerns regarding masitinib. The company intends to complete these clinical studies in accordance with applicable regulations. Stéphane Ledermann, Chairman and CEO of AB Science, stated, “This decision to terminate non-priority studies for which recruitment had been suspended and for which there is no prospect of a rapid resumption reflects compliance with regulatory requirements. It is also consistent with our commitment to allocate all necessary resources to ensure the two priority programs are carried out to the highest standards of quality .” Regarding the AB8939 program for acute myeloid leukemia, the company announced [2] the completion of Phase 1, Step 3, evaluating the combination of AB8939 and venetoclax. The next step is to seek authorization from health authorities—based on a preliminary favorable opinion from the study’s Independent Data Monitoring Committee (IDMC)—to initiate Phase 4 of the study, which will evaluate the triple combination of AB8939, venetoclax, and azacitidine. Regarding the Phase 3 program for masitinib in amyotrophic lateral sclerosis, which was approved in 2025 [3] but has not yet begun, the company will update the protocol and its implementation procedures, and will seek authorization from health authorities to resume this study after submitting a substantial amendment. [1] Press release dated April 16, 2026 [2] Press release dated June 29, 2026 [3] Press release dated July 24, 2025 About AB23005 in ALS The AB23005 study is a prospective, multicenter, randomized, double-blind, placebo-controlled, two-arm study conducted in patients with amyotrophic lateral sclerosis (ALS), designed to confirm the efficacy and safety of masitinib (at a dose of 4.5 mg/kg/day in combination with riluzole) compared to riluzole plus placebo after 48 weeks of treatment. The study will include 408 patients (randomized in a 1:1 ratio) with ALS who are experiencing normal disease progression (i.e., a functional decline of less than 1.1 points per month) and who have not experienced a complete loss of function (i.e., a score of at least 1 on each of the 12 items of the ALSFRS-R scale). U.S. patients receiving edaravone will also be eligible to participate in the study, as the use of this medication constitutes a stratification factor. About AB18001 in AML The AB18001 study, titled “A Phase 1/2 Study to Evaluate the Safety, Pharmacokinetics, and Efficacy of AB8939 Administered Intravenously Daily in Patients with Relapsed/Refractory Acute Myeloid Leukemia , ” is designed in several phases. The first part is a dose-escalation study designed to assess the safety and tolerability of AB8939 and to determine the recommended dose for the Phase 2 expansion study. The objective of the Phase 1 study is to determine the maximum tolerated dose (MTD) for the different treatment regimens with AB8939. Phase 1: Determination of the MTD after 3 consecutive days of treatment with AB8939 alone. Phase 2: Determination of the MTD after 14 consecutive days of treatment with AB8939 alone. Phase 3: Determination of the MTD after 14 consecutive days of treatment with AB8939 in combination with venetoclax. Phase 4: Determination of the maximum tolerated dose (MTD) after 14 consecutive days of treatment with AB8939 in combination with venetoclax and azacitidine. About AB Science Founded in 2001, AB Science is a pharmaceutical company specializing in the research, development, and commercialization of protein kinase inhibitors (PKIs), a class of targeted proteins that play a critical role in cellular signaling. Our programs target only diseases with high unmet medical needs—often fatal conditions with low survival rates, rare diseases, or those resistant to first-line treatment. AB Science has independently developed a portfolio of molecules, and its lead compound, masitinib, has already been approved for veterinary use and is currently undergoing clinical development in humans. The Company is headquartered in Paris and is listed on Euronext Paris (Ticker: AB). For more information about the Company, visit the website: Forward-Looking Statements – AB Science This press release contains forward-looking statements. These statements are not historical facts. They include projections and estimates, as well as the assumptions on which they are based, and statements regarding plans, objectives, intentions, and expectations concerning future financial results, events, operations, services, product development and potential, or future performance. These forward-looking statements can often be identified by the words “expect,” “anticipate,” “believe,” “intend,” “estimate,” or “plan,” as well as by other similar terms. Although AB Science believes that these forward-looking statements are reasonable, investors are cautioned that such statements are subject to numerous risks and uncertainties—which are difficult to predict and generally beyond AB Science’s control—that may cause actual results and events to differ materially from those expressed, implied, or projected in the forward-looking information and statements. These risks and uncertainties include, in particular, uncertainties inherent in the development of the Company’s products—which may not be successful—or in the granting of marketing authorizations by the competent authorities, or, more generally, any factors that may affect the ability to commercialize the products developed by AB Science, as well as those developed or identified in public documents published by AB Science. AB Science makes no commitment to update forward-looking information and statements, subject to applicable regulations, in particular Articles 223-1 et seq. of the AMF’s General Regulations. For further information, please contact: AB Science Financial Communications investors@ab-science.com Attachment Clinical Program Update July 2026 VENG VF

iStock, Andrii Yalanskyi The trials, which were testing the tyrosine kinase inhibitor masitinib, had previously been paused. AB Science’s decision not to resume them was a matter of prioritization, not safety, the biotech said. AB Science is formally terminating three studies for immune-mediated diseases in what it characterizes as an effort to better focus the biotech’s resources on its priority programs. The French company is axing a mid-stage study in mast cell activation syndrome (MCAS), a late-stage trial in mastocytosis and a Phase 3 study in progressive multiple sclerosis, according to a news release on Friday . All three trials were testing the tyrosine kinase inhibitor masitinib. AB Science designated these three programs as “non-priority,” with CEO Stéphane Ledermann noting in a Friday statement that enrollment for the trials had previously been paused and “there is no prospect of a rapid resumption.” The company emphasized that the decision to discontinue the three studies was not driven by safety issues with masitinib. AB Science promised to complete the trials “in accordance with applicable regulations.” MCAS and mastocytosis are rare immunological diseases involving dysfunctional mast cells, white blood cells specifically involved in warding off infections. These cells are hyperactivated in MCAS, releasing immune factors even without a trigger, in turn manifesting as diarrhea, rashes, shortness of breath and, in severe cases, anaphylaxis. Mastocytosis, meanwhile, occurs when mast cells accumulate in the skin, bone marrow and other organs. Symptoms of the two conditions overlap, though mastocytosis can worsen to cancer and organ damage. Multiple sclerosis is an autoimmune disease that arises when the body attacks the protective covering of nerves, leading to motor problems, numbness, vision loss and other complications. AB Science will now dedicate much of its focus to its two main clinical programs. One will test masitinib for amyotrophic lateral sclerosis (ALS) while the other will focus on an investigational microtubule destabilizer, dubbed AB8939 , for acute myeloid leukemia. Last month, the biotech announced that AB8939, when combined with Roche and AbbVie’s Venclexta, elicited a 67% overall response rate in a Phase 1 study of patients with relapsed or refractory disease. The company is now moving the candidate to the next part of the early trial, looking at combining AB8939 with Venclexta and the chemotherapy azacitidine. According to the biotech’s website , there remain two other masitinib programs: a Phase 3 trial in Alzheimer’s disease and a Phase 2 study for sickle cell disease. AB Science also has a preclinical candidate for sarcoma and solid tumors.