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Purpose: This phase 1, open-label, single-arm clinical trial evaluated pharmacokinetics, safety, and biomarker activity of palbociclib-letrozole as first-line treatment for estrogen receptor-positive/human epidermal growth factor receptor 2-negative advanced breast cancer (ABC) in postmenopausal Chinese women to support palbociclib approval in China.Methods: Patients received palbociclib 125 mg once daily (3/1 schedule) plus letrozole 2.5 mg once daily. Blood samples were collected predose and ≤ 120 h after single and multiple doses of palbociclib. The incidence and severity of adverse events were reported. Skin biopsy tissues and blood samples were collected for biomarker assessments.Results: By 31 July 2018, 26 patients were enrolled. After single and multiple dosing, palbociclib maximum plasma concentration was 82.14 and 139.7 ng/mL, apparent clearance was 52.40 and 49.97 L/h, AUCτ was 1217 and 2501 ng∙h/mL, and t½ was 23.46 and 27.26 h, respectively. Levels of Ki67, retinoblastoma protein, and thymidine kinase decreased after palbociclib treatment. A similar safety profile as previously reported was observed.Conclusions: Pharmacokinetic and pharmacodynamic effects of palbociclib were well characterized in Chinese patients with ABC. Despite higher exposure, pharmacokinetic parameters were similar to those of a previously studied non-Asian population. No palbociclib dose adjustment based on Chinese ethnicity is needed. Palbociclib-letrozole had a manageable safety profile.Clinical Trial Registration: NCT02499146. [ABSTRACT FROM AUTHOR]