The recommended dose in Japanese patients—based on a phase 1 study of palbociclib in Japanese patients with advanced ER+/HER2– breast cancer—is 125 mg palbociclib once daily (3 weeks on/1 week off [i.e., 3/1 schedule]) in combination with 2.5 mg letrozole [18], the same as Western patients. Here, ESR1 is linked to breast carcinoma.