Hormone therapy is the primary treatment option for patients with HR+ HER2- breast cancer. Despite its activity, hormone therapy is associated with initial, or more frequently acquired, resistance after exposure to one or more treatment lines.

The combination of palbociclib with hormone therapy significantly increases progression free survival (PFS) compared with hormone therapy in first and second treatment line of HR+ HER2- advanced breast cancer.

These results lead to palbociclib approval by the Food and Drug Administration (FDA) in February 2015, and European Medicines Agency (EMA) approval in November 2016 for first-line treatment of patients with metastatic HR+/HER2-breast cancer in combination with an aromatase inhibitor, and for patients who had previously received hormone therapy in combination with fulvestrant.

In Spain, palbociclib was launched last November 1st, 2017. During this period, approximately 3500 patients have received treatment with Palbociclib, and approximately a half of them in first-line treatment in combination with hormone therapy. The collection of efficacy and toxicity data in the first-line usage in the clinical practice setting is of clinical interest.

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-

  1. HR+: ER+ or PR+ test before or up to 60 days after MBC diagnosis
  2. 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 available.

• 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

Patients with advanced or metastatic breast cancer receiving palbociclib in first line in 35 Hospitals from Spain.