Optimal treatment for aromatase inhibitor-resistant metastatic breast cancer patients: lessons from the PEARL study

Hormone receptor-positive (HR+), HER2-negative (HER2−) tumors represent ∼70% of metastatic breast cancer (mBC) patients. Endocrine treatment (ET) in combination with cyclin-dependent kinase 4-6 inhibitors (CDK4/6is) is the standard of care in first line, and an effective treatment option in second and subsequent lines.1 Palbociclib was the first-in-class CDK4/6i to be approved, both in combination with letrozole as first-line treatment for HR+/HER2− mBC, based on the results of PALOMA-2, and in combination with fulvestrant in patients with HR+/HER2− mBC after progression to ET, based on the results of PALOMA-3.