Inclusion Criteria:  1. Documented histologically confirmed breast cancer with ER and/or PgR positive and HER2 negative status. 2. Locally advanced or metastatic breast cancer not deemed amenable to curative surgery or curative radiation therapy  3. HR+/HER2-  HR+: ER+ or PR+ test before or up to 60 days after MBC diagnosis HER2-: any HER2 negative test and the absence of a positive test (IHC positive 3+, FISH positive/amplified, Positive NOS) before or up to 60 days after MBC diagnosis 4. Female or male patients > 18 years 5. Have received at least one dose of palbociclib 6. At least 2 document clinical visits 7. Treatment with palbociclib should have started from November 2017 to November 2019 8. Data from the clinical records should be avaliable. 9. Patients must be able to understand and sign informed consent if alive.  Exclusion Criteria:  1. Previous treatment with hormonal therapy, targeted therapy or chemotherapy for metastatic disease. Previous anticancer treatment for early breast cancer are allowed. 2. Treatment with palbociclib in clinical trial or compassionate use programs 3. HER2 + (IHC 3+ or FISH +) tumors in the most recent or previous biopsies 4. HR negative tumors in the most recent biopsy