This is a Phase Ib open-label, 2-Part, multi-center study in China. The study will be conducted in two stages: Stage 1 is the dose-escalation part, which is designed to evaluate the safety, tolerability, PK and efficacy, as well as to determine the maximum tolerable dosage (MTD) or maximum applicable dose (MAD) of HS-10352 in combination with fulvestrant. Stage 2 is the dose-expansion part, which is aimed to further assess the efficacy, safety, tolerability and PK, and to establish the recommended phase 2 dose (RP2D) of HS-10352 in combination with fulvestrant.~All participants will be carefully monitored for adverse events (AE) during the study treatment and for 28 days after the last dose of study drug. The PK characteristics of HS-10352 and fulvestrant will be evaluated from C1 to C6. Subjects of this study will be assessed for progression once every 8 weeks until objective disease progression or withdrawal from the trial. As the disease progresses, survival follow-up is recommended bimonthly.
HS-10352 is a highly potent and selective small molecule inhibitor of phosphoinositide 3-kinase (p110α). The purpose of this study is to assess the safety, tolerability, pharmacokinetics (PK), and efficacy of HS-10352 plus fulvestrant in patients with hormone receptor (HR) positive, human epidermal growth factor 2 (HER2)-negative, advanced breast cancer (ABC) harboring PIK3CA mutations.