Aptevo Therapeutics Inc. (NASDAQ:APVO) shares plunged about 18% on Tuesday even after the company reported promising interim clinical results for its acute myeloid leukemia (AML) treatment candidate, mipletamig.
The clinical-stage biotech said mipletamig, when combined with venetoclax and azacitidine, achieved an 86% clinical benefit rate in newly diagnosed AML patients who are elderly or considered unsuitable for intensive chemotherapy. The company also reported that no cases of cytokine release syndrome were observed among frontline patients receiving the treatment.
Data from 28 evaluable frontline patients enrolled in the RAINIER study and a completed dose expansion trial showed that 79% of patients achieved either complete remission or complete remission with incomplete blood count recovery. Of those, 61% reached complete remission. Additionally, 55% of patients who entered remission experienced blast reductions that reached measurable residual disease-negative levels.
The company said four patients treated in the program have so far proceeded to allogeneic stem cell transplantation. It also noted that 35% of patients who achieved remission carried the TP53 mutation, a high-risk genetic marker commonly associated with poor outcomes in AML.
“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, Chief Medical Officer of Aptevo Therapeutics.
The RAINIER trial is a Phase 1b/2 multicenter study designed to optimize dosing. It is enrolling adults aged 18 and older with newly diagnosed AML who are not candidates for intensive induction chemotherapy. The Phase 1b portion includes 28-day treatment cycles across sequential patient cohorts.
Despite the encouraging clinical findings, the sharp decline in Aptevo’s share price suggests investors may be focused on concerns around the company’s path toward commercialization or potential funding requirements.