• Men or women aged more than or equal to (≥) 18 years

• HR+ HER2- breast cancer confirmed by histology or cytology.

• Locally advanced disease not amenable to curative treatment by surgery or metastatic disease.

• Have adequate tumor tissue for the analysis of PIK3CA mutational status. At dose expansion stage, participants should be identified as PIK3CA-mutation positive before enrollment.

• Females should have postmenopausal status due to either surgical/natural menopause or ovarian suppression with a luteinizing hormone releasing hormone (LHRH) agonist before enrollment. Males should be pre-treated with a LHRH agonist.

• Have either measurable disease per RECIST v1.1 criteria or at least one predominantly lytic bone lesion must be present.

• ECOG performance status was 0-1 and did not deteriorate in the previous 2 weeks.

• Estimated life expectancy for at least three months

• Females should be using adequate contraceptive measures and should not be breastfeeding at the time of screening, during the study and until 6 months after completion of the study; and have negative results of blood pregnancy test prior to C1D1.

• Males should be using adequate contraceptive measures at the time of screening, during the study and until 6 months after completion of the study.

⁃ Have signed Informed Consent Form

⁃ Dose escalation stage-Cohort 1: subjects resistant to endocrine therapy Dose expansion stage-Cohort 2: subjects resistant to endocrine therapy Dose expansion stage-Cohort 3: endocrine therapy-sensitive or endocrine-naive subjects