This national UK study was designed with the aim of collecting a significantly large scale real-world dataset of patients aged ≥75 years to evaluate the tolerability, efficacy and secondary care in-patient burden in the National Health Service (NHS) when palbociclib is used in combination with an AI in the first-line treatment of elderly patients with ER+/HER2-advanced breast cancer. This evidence concerns the gene ERBB2 and breast carcinoma.