Aptevo Therapeutics Inc. announced new remission data on four additional patients. The new data includes one patient who achieved a complete remission (CR), one patient who achieved a complete remission with incomplete hematologic recovery (CRi) and two patients who achieved bone marrow complete remissions, or morphological leukemia-free state (MLFS), in the Company's on-going multi-cohort, multi-center Phase 1b expansion trial evaluating APVO436 for the treatment of acute myeloid leukemia (AML). The Company also provided an update on a myelodysplastic syndrome (MDS) patient from the dose escalation part of the trial.

Cohort 1 currently has the highest enrollment rate in the trial and preliminary data show that a total of four out of 11 response-evaluable patients (36%) reported on to date, have experienced remission while on therapy. Of the three new cohort 1 patients announced today, one is a CR, one is a CRi, and one is a bone marrow complete remission (MLFS). Cohort 1 is a combination arm of the trial that includes relapsed patients and those with primary refractory AML that failed to respond to frontline standard induction chemotherapy.

Cohort 1 patients receive standard chemotherapy drug cytarabine or the standard chemotherapy triple drug combination MEC (mitoxantrone, etoposide, cytarabine) plus APVO436. The Company also announced that a patient with high-risk myelodysplastic syndrome (MDS) enrolled in the dose escalation trial remains stable and continues treatment with APVO436 now exceeding 18 months. Prior to joining the trial, this patient received and failed treatment with a hypomethylating agent, a situation that is commonly expected to be a poor prognostic event associated with short survival probability of approximately four to six months.

In this study, a “complete remission (CR)” is defined as a patient with no evidence of leukemia after treatment. This means the bone marrow contains < 5% leukemic blasts and hematologic (blood) recovery that includes normal white blood cell and platelet counts and other markers of healthy blood. A “CRi” is defined as a complete remission except for residual thrombocytopenia or neutropenia.

A “bone marrow complete remission (MLFS)” is defined as bone marrow blasts consistent with complete remission, <5%, but where peripheral blood recovery has not yet been observed.