This research was the starting point for the clinical trial PALOMA-1 (open-label, randomized, proof-of-concept study) that showed significantly longer progression-free survival for letrozole (an aromatase inhibitor, standard treatment for postmenopausal women with HR+/HER2- breast cancer) in combination with palbociclib than letrozole alone [33]. The gene discussed is CYP19A1; the disease is breast cancer.