Aptevo Therapeutics Inc. (Nasdaq: APVO) reported a 93% clinical benefit rate in a small group of frontline acute myeloid leukemia (AML) patients with TP53 mutations treated with its mipletamig drug candidate in combination with venetoclax and azacitidine, according to a company statement.

Of 14 evaluable patients treated with the triplet combination, 13 experienced clinical benefit. Eleven patients, or 79%, achieved complete remission (CR) or complete remission with incomplete hematologic recovery (CRi), including nine complete remissions.

The company compared the 79% CR/CRi rate to a published 41% composite remission rate for venetoclax plus azacitidine alone in treatment-naïve patients with poor-risk cytogenetics and TP53-mutated AML, based on a 2022 study published in Clinical Cancer Research by Pollyea et al.

"TP53-mutated AML remains one of the most challenging AML subpopulations to treat," said Dirk Huebner, M.D., Chief Medical Officer of Aptevo. "Seeing this level of clinical benefit with the mipletamig triplet in a patient population that historically has not responded well to treatment is exciting."

The data includes two patients from a previously completed dose expansion trial. Clinical benefit in this context includes complete remission, complete remission with incomplete hematologic recovery, partial response, and morphologic leukemia-free state.

Aptevo's ongoing RAINIER study is a Phase 1b/2 dose optimization trial evaluating mipletamig in combination with venetoclax and azacitidine in frontline AML patients who are not eligible for standard high-intensity chemotherapy. The dose optimization phase is expected to conclude by year-end 2026, with regulatory interaction planned for the first half of 2027.

Mipletamig has received orphan drug designation for AML under the Orphan Drug Act. The small patient sample size and early-stage nature of the trial mean results may differ in later-stage studies.