Physician inclusion criteria:  Oncologist or gynecologist. Responsible for treating ≥4-10 (depending on country) ABC/MBC patients who meet the eligibility criteria. Agrees to participate in the study and complete the case report forms (CRFs) within the data collection period.  Patient inclusion criteria:  HR+/HER2- breast cancer diagnosis with confirmed metastatic or advanced disease. Received palbociclib as a first line therapy. No prior or current enrolment in an interventional clinical trial for ABC/MBC. Minimum of six months of follow up data since palbociclib initiation.  Physician exclusion criteria:  Qualified less than 2 years ago or more than 35 years ago. Participated in observational research for ABC/MBC in the last 3 months. Have not prescribed either palbociclib plus fulvestrant or palbociclib plus aromatase inhibitor as first line therapy.