Pharmacokinetics, safety, activity, and biomarker analysis of palbociclib plus letrozole as first-line treatment for ER+/HER2- advanced breast cancer in Chinese women.

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.