A First-in-Human Study of Mutant-selective PI3Kα Inhibitor, RLY-2608, As a Single Agent in Advanced Solid Tumor Patients and in Combination with Fulvestrant in Patients with Advanced Breast Cancer

This is an open-label, FIH study designed to evaluate the maximum tolerated dose, recommended Phase 2 dose, safety, tolerability, PK, pharmacodynamics, and preliminary antineoplastic activity of RLY-2608, in advanced solid tumor patients with a Phosphatidylinositol-4,5-bisphosphate-3 kinase, catalytic subunit alpha (PIK3CA) mutation in blood and/or tumor per local assessment. The study will evaluate RLY-2608 as a single agent for patients with unresectable or metastatic solid tumors. It will also evaluate RLY-2608 in combination RLY-2608 + fulvestrant and in triple combination RLY-2608 + fulvestrant + CDK4/6 inhibitor (palbociclib or ribociclib) or CDK4 inhibitor (PF-07220060) for patients with HR+ HER2- locally advanced or metastatic breast cancer or endometrial cancer (palbociclib or ribociclib Part 1). The RLY-2608 single agent arm, RLY-2608 + fulvestrant combination arm, and triple combination arms will have 2 parts: a dose escalation (Part 1) and a dose expansion (Part 2).