HS-10352 in hormone receptor-positive, HER2-negative advanced breast cancer: A phase 1 dose-escalation trial

Background: Approximately 40% of patients with hormone receptor (HR)-positive and human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer (ABC) exhibit PIK3CA mutations.Aims: This study aims to evaluate the safety, tolerability, pharmacokinetics, and preliminary antitumor activity of HS-10352, a selective PI3K alpha inhibitor, in this patient population.Materials and Methods: Conducted as a phase 1 dose-escalation trial, HS-10352 was administered orally once-daily (QD) at dose levels of 2, 4, 6, and 8 mg. The primary endpoints were dose-limiting toxicity (DLT) and the maximum tolerated dose (MTD). This study is registered at ClinicalTrials.gov (NCT04631835).Results: Between August 2020 and March 2022, a total of 18 female patients were enrolled. DLT, manifested as hyperglycemia, occurred in two patients in the 8 mg QD group, establishing an MTD of 6 mg QD. The most common treatment-related adverse events were hyperglycemia (88.9%) and weight loss (61.3%). In the 6 mg QD group, four patients (66.7%) had a partial response (PR), and one (16.7%) had stable disease (SD). Among the four patients with PIK3CA mutated tumors in this dosage group, three (75.0%) had PR and one (25.0%) had SD. The median progression-free survival was not reached (95% confidence interval, 11.1-NA).Discussion and Conclusion: HS-10352 at 6 mg QD was well-tolerated in patients with HR-positive, HER2-negative ABC, and showed preliminary antitumor activity in patients with PIK3CA mutated tumors. These findings support the further clinical development of HS-10352.