Palbociclib plus exemestane with gonadotropin-releasing hormone agonist versus capecitabine in premenopausal women with hormone receptor-positive, HER2-negative metastatic breast cancer (KCSG-BR15–10): a multicentre, open-label, randomised, phase 2 trial - Park, YH; Kim, TY; Kim, GM (Lancet Oncol, 2019)