Aptevo Therapeutics Inc. announced that its bispecific AML drug candidate APVO436, in combination with emerging standard of care venetoclax and azacitidine, achieved positive duration of remission results in its Phase 1b dose escalation trial. The Company is also providing an update of its APVO436 Phase 2 program design that will include both frontline and relapsed/refractory trials beginning later in the second half of 2023. Duration of Remission (DOR) Positive and clinically meaningful DOR results was observed from the company's bispecific AML drug candidate APVO436 in combination with the emerging standard of care (venetoclax + azacitidine) in venetoclax treatment naïve patients, as follows: High response rate observed - 82% (9/11) of patients had a favorable response and were eligible for inclusion in the DOR analysis; Multiple patients moved to transplant - 3/11 patients responded sufficiently to move to stem cell transplant - receiving stem cell transplant is the treatment option with the best probability for survival and highest benefit to patients; Sustained complete response -Of the patients with responses, one patient remained on study with sustained complete response for 8 cycles (the maximum allowed per protocol) which translated into at least 8 months of response duration; Median DOR not reached - The median DOR was not reached, which is clinically meaningful because a substantial number of patients either stayed on treatment or moved to transplant and did not experience a relapse event.

This DOR data adds to a growing body of clinical evidence (safety, tolerability, efficacy and now durability), that provides strong support for the further development of APVO436 in combination therapy for patients with AML. Phase 2 Program Update: The Company's APVO436 Phase 2 program will further evaluate the triplet combination of APVO436 + venetoclax + azacitidine among frontline and relapsed/refractory AML patients who are venetoclax treatment naïve. The Company intends to conduct two trials.

The first, among relapsed/refractory patients, will initiate in second half 2023. The second, among frontline patients, will initiate in first half 2024. Aptevo anticipates that approximately 100 patients will participate between the two trials and that interim results will be available in late second half 2024.

APVO436 Dose Escalation Trial Results: Safety and Efficacy Data (previously reported): Efficacy: APVO436 demonstrated a 91% clinical benefit* in combination with venetoclax + azacitidine in venetoclax treatment naïve patients, more than doubling the response rate in a composite benchmark across all benefit categories; Safety: APVO436, when given in combination with this regimen, has been shown to be generally safe and well tolerated. Cytokine Release Syndrome(CRS), a common side effect in other trials,was observed in fewer than one quarter of patients within the patient population and in most cases was mild or moderate (grade 1 or 2) and was manageable in the clinic.