ERBB2 and breast cancer: The PALOMA-1 study (NCT00721409) was a multicenter, randomized phase I/II study, whereby postmenopausal patients with HR-positive, HER2-negative breast cancer were treated with palbociclib (at a dose of 125 mg orally daily on the 3/1 schedule) combined with letrozole 2.5 mg daily continuously versus letrozole alone [65].