A Phase ll, Interventional, Single-arm Study Evaluating the Efficacy and Safety of Inavolisib Plus Ribociclib and Fulvestrant in Chinese Patients With PIK3CA-mutant, HR-positive, HER2-negative Locally Advanced or Metastatic Breast Cancer.

This is a prospective, multicenter, open-label, single-arm phase II investigator-initiated study designed to evaluate the efficacy and safety of inavolisib in combination with ribociclib and fulvestrant as first-line treatment in Chinese patients with PIK3CA-mutant, hormone receptor-positive (HR+), HER2-negative (HER2-), endocrine-resistant metastatic breast cancer (mBC). Approximately 160 patients will be enrolled at around 16 centers in China. The study consists of a screening period of up to 28 days, a treatment period, and a post-treatment follow-up period. PIK3CA mutation status must be determined in blood or tumor tissue using polymerase chain reaction (PCR)-based assays or next-generation sequencing (NGS) performed in a local clinical laboratory. Patients with locally confirmed PIK3CA mutations who meet all eligibility criteria will be enrolled and receive study treatment with inavolisib, ribociclib, and fulvestrant. Details of the treatment regimen are provided in the Study Treatment section. Study treatment will continue until radiologically confirmed disease progression as determined by the investigator, unacceptable toxicity, withdrawal of informed consent, or study termination, whichever occurs first. Patients must have measurable disease according to RECIST v1.1. Patients with bone-only metastases are not eligible, even if the lesions are considered measurable. Locally advanced disease must be unsuitable for surgical resection or other local treatment with curative intent.