The main purpose of this study is to evaluate the effectiveness of inavolisib based regimen in participants with endocrine-resistant, phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha gene (PIK3CA)-mutated, hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) locally advanced or metastatic breast cancer (LA/mBC), following on or after completing adjuvant endocrine therapy in routine clinical practice in China.

Inclusion Criteria:

• Participants must be diagnosed with endocrine-resistant, PIK3CA-mutated, HR+/HER2- LA/mBC, following recurrence on or after completing adjuvant endocrine therapy
• Participants must receive the treatment of inavolisib for the first time
• PIK3CA mutation status should be detected by a National Medical Products Administration (NMPA)-approved or validated assay [Polymerase Chain Reaction (PCR) or Next Generation Sequencing (NGS)] by testing of blood or tumor tissue prior to the initiation of inavolisib

Exclusion Criteria:

• Participants for which the treatment with inavolisib is not indicated per prescribing information. If the participant starts palbociclib and fulvestrant first, and starts inavolisib after getting a PIK3CA mutation-positive test result later, the palbociclib and fulvestrant will not be deemed as a different line of therapy. However, the medical order of PIK3CA mutation test must be made before or at the same time with the prescription of palbociclib and fulvestrant
• Participants not receiving treatment for LA/mBC with inavolisib according to standard of care (SOC) and in line with the current summary of product characteristics (SPC)/local labeling
• At the investigator's discretion, any reason that makes the participant hard to follow up or unsuitable to participate in the study

Participants with endocrine-resistant, PIK3CA-mutated, HR+, HER2-, LA/mBC, following on or after completing adjuvant endocrine therapy in routine clinical practice in China.