Inclusion Criteria:  Signed informed consent from the patient or a legally acceptable representative, obtained before any study-related activities are undertaken Patients diagnosed with HR+, HER2- locally advanced or metastatic breast cancer with a PIK3CA mutation Patients who have disease progression following endocrine therapy as monotherapy Patients must be postmenopausal women, or men, ≥18 years of age Patients recruited on or before their first prescribed dose of alpelisib in combination with fulvestrant  Exclusion Criteria:  Use of alpelisib prior to signing the informed consent form for this study Participation in an interventional study within 30 days prior to the initiation of alpelisib