Real-world effectiveness and sensitivity of palbociclib plus endocrine therapy in HR+/HER2– patients with metastatic breast cancer

Palbociclib has shown satisfactory outcomes when combined with endocrine therapy (ET) in hormone receptor-positive and human epidermal growth factor receptor 2-negative (HR+/HER2-) metastatic breast cancer (MBC). However, data in Asia are currently scarce.This retrospective study aimed to evaluate the real-world effectiveness, sensitivity, and toxicity of palbociclib plus ET in HR+/HER2- MBC in North China. We recruited patients with HR+/HER2- MBC from August 2018 to July 2020 across 7 hospitals in North China. The primary endpoint was to evaluate progression-free survival (PFS) after initial progress on palbociclib therapy. The secondary endpoints included determining predictive biomarkers of palbociclib sensitivity and toxicity of palbociclib.A total of 54 patients were analyzed in this cohort with an estimated median follow-up time of 14.3 months. Patients who received palbociclib as a first-line treatment showed significantly prolonged PFS compared with those who received palbociclib as a second-line or beyond treatment (21.8 months vs 15.9 months vs 6.8 months) (P < .001). Besides, patients with Ki67 <30% (P = .024) and PR ≥20% (P = .041) in metastatic tumors had significantly longer PFS. The Cox proportional-hazards regression analyses proved that different lines (P = .001 in multivariate analysis), Ki67 <30% (P = .035 in multivariate analysis), and PR ≥20% (P = .045 in univariate analysis) in metastatic tumors affected PFS significantly. The most common adverse events were hematologic, with 31.48% of patients having neutropenia.Palbociclib plus ET significantly prolonged PFS for patients with HR+/HER2- MBC who received first-line therapy, with manageable toxicity. The values of Ki67 and PR in metastatic tumors may be potential predictive biomarkers of palbociclib sensitivity.