Aptevo Announces New mipletamig Data with 86% Clinical Benefit Rate

Aptevo Therapeutics announced new interim data for mipletamig in combination with venetoclax and azacitidine in newly diagnosed acute myeloid leukemia patients who are either elderly or unfit for intensive chemotherapy. In data from two trials, the combination has demonstrated robust clinical activity, delivering an 86% clinical benefit rate with zero patients experiencing the common symptom of cytokine release syndrom. These data support an emerging efficacy profile coupled with differentiated patient safety and tolerability that is additive to the current AML standard-of-care therapy. "The emerging mipletamig data in frontline AML are highly encouraging and highlight the differentiated profile we believe is needed to advance treatment in frontline AML," said Dirk Huebner, CMO. "In this study we are observing strong remission rates in a growing number of evaluable patients together with a consistently favorable safety and tolerability profile, including the absence of cytokine release syndrome. Achieving meaningful clinical activity while maintaining this level of safety and tolerability is essential in the frontline AML setting, where therapies must be compatible with established regimens. These results reinforce our belief that mipletamig can be successfully combined with venetoclax and azacitidine, with the potential to enhance outcomes for older and/or unfit AML patients who continue to face poor prognosis and limited treatment options. Importantly, four of the patients treated to date have proceeded to allogeneic stem cell transplant, which represents the best possible outcome in AML treatment and is rarely achieved in the older or unfit frontline patient population." Data Highlights Include: Among the evaluable frontline patient population treated to date, including 24 patients from the RAINIER trial and 4 patients from the completed dose expansion trial, mipletamig in combination with venetoclax and azacitidine has demonstrated: 100% of frontline patients have remained free of cytokine release syndrome; 86% clinical benefit rate; 79% achieved CR or CRi; 61% achieved CR; 55% of patients who achieved CR/CRi had blast reductions that reached the important measurable residual disease-negative level, a result that is typically associated with stronger, more durable responses; 35% of patients with remissions had the TP53 genetic mutation, a high-risk biomarker typically associated with poor prognosis in AML and for which most treatment options frequently fail. Collectively, these data demonstrate mipletamig's potential to meaningfully enhance frontline AML treatment in older and/or unfit patients, by improving efficacy outcomes without materially increasing toxicity.