A phase Ib/II study of mirdametinib in combination with palbociclib in patients with advanced dedifferentiated liposarcoma.

Abstract

TPS11594 Background: Dedifferentiated liposarcoma (DDLPS) is a rare adipocytic malignancy characterized by frequent amplification of MDM2 and CDK4 and associated with poor outcomes, with a median overall survival of approximately 15 months. A phase II trial at Memorial Sloan Kettering Cancer Center demonstrated activity of the CDK4/6 inhibitor palbociclib in advanced WD/DDLPS, with a 12-week progression-free survival (PFS) rate of 57%, exceeding historical chemotherapy benchmarks (<35%) and leading to its inclusion in the NCCN Guidelines. Despite this, durability of benefit remains limited, and outcomes following progression are poor. Preclinical work from our group demonstrated that CDK4/6 inhibition in DDLPS induces cellular geroconversion from quiescence to irreversible senescence, accompanied by MDM2 downregulation. This process requires suppression of HRAS signaling and inhibition of the MAPK pathway and is associated with activation of the senescence-associated secretory phenotype (SASP). Preclinical models further suggest that dual CDK4/6 and MEK inhibition enhances SASP activation, providing a mechanistic rationale for combination therapy. Based on these findings, we initiated a phase Ib/II clinical trial of mirdametinib, a MEK1/2 inhibitor, in combination with palbociclib in patients with DDLPS (NCT06843967). Methods: This is an ongoing phase Ib/II, single-arm, open-label, single-center study evaluating the safety, tolerability, and efficacy of mirdametinib plus palbociclib in patients with unresectable, recurrent, or metastatic DDLPS (NCT06843967). Patients may enroll at any line of therapy, including first line, consistent with contemporary palbociclib use; patients with prior CDK4/6 inhibitor exposure are eligible for the phase Ib portion. Key eligibility criteria include ECOG performance status 0–2 and RECIST v1.1–measurable disease. Phase Ib uses a Bayesian optimal interval (BOIN) design with three dose levels to determine dose-limiting toxicities, maximum tolerated dose, and recommended phase II dose (RP2D), enrolling up to 24 patients. Phase II will assess efficacy at the RP2D, with the primary endpoint of PFS at 18 weeks by RECIST v1.1 in 30 patients. Enrollment began February 19, 2025. As of January 2026, accrual is ongoing at dose level 2. Enrollment to dose level 3 is anticipated in February 2026. Clinical trial information: NCT06843967 .