SOUTH SAN FRANCISCO - Sutro Biopharma, Inc. (Sutro or the Company) (NASDAQ: STRO), a clinical-stage oncology company pioneering site-specific and novel-format antibody drug conjugates (ADCs),today announced that its research collaborators presented data on anti-leukemic activity from the compassionate use of luveltamab tazevibulin (luvelta), a novel folate receptor- (FR-) targeting ADC, in pediatric patients with relapsed/refractory CBFA2T3-GLIS2 (CBF/GLIS) acute myeloid leukemia (AML), commonly known as RAM phenotype AML.

Data demonstrated that treatment with luvelta produced meaningful clinical responses, including complete remission (CR) and prolongs overall survival (OS) enabling some patients to receive potentially curative therapies such as hematopoietic stem cell transplant. These patients were treated under the single patient IND mechanism. These data were featured in a poster presentation at the 65th American Society of Hematology Annual Meeting and Exposition (ASH 2023) in San Diego, CA.

Treatment with luvelta led to notable response in a significant subset of patients who had exhausted all therapeutic options, said Soheil Meshinchi, M.D., Ph.D., presenter and primary author. Response varied from deep remissions to disease stabilization with minimal toxicity - mostly in outpatient setting. Luvelta was well tolerated as long-term maintenance therapy with little to no hematopoietic toxicity.

CBF/GLIS subtype AML is a rare and highly lethal form of leukemia found exclusively in infants and young children, with the average age of onset at 18 months 1. There are no therapies specifically approved to target this form of leukemia and it is resistant to conventional chemotherapy, with an induction failure rate of over 80%2. Due to a lack of effective treatment, children diagnosed with the disease have a dismal two-year survival rate of 15%3. Recent studies have shown that FOLR1, which encodes for FolR, is silent in normal hematopoiesis, but is uniquely induced by the CBF/GLIS fusion4.

Under compassionate use, 25 pediatric patients with relapsed/refractory CBF/GLIS subtype AML were treated with luvelta at doses up to 4.3 or 5.2mg/kg every two to four weeks for a median duration of 15.9 weeks (3-73.1), with the majority of patients receiving at least five doses (68%). Of the 25 treated patients, 19 had 5% blasts (morphologic disease, or MD) and 8 had

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