LAUSR

BACKGROUND In patients with hormone receptor positive metastatic breast cancer, Palbociclib has been shown to improve overall survival and progression-free survival (PFS) when combined with endocrine therapy. Dose modification of palbociclib is effective in the management of adverse events. Despite variable clinical response, no predictive biomarkers of efficacy to palbociclib have been identified in metastatic breast cancer. In our study, we aimed to assess the PFS of metastatic breast cancer patients who received dose-reduced palbociclib and compare the results in the non-dose reduced group. We also evaluated the clinical significance of progesterone receptor (PR) and Ki67 as predictive biomarkers of palbociclib. METHODS Seventy-six palbociclib-treated metastatic breast cancer patients were included in our study. PFS was compared between dose reduced and non-dose reduced groups. PR expression and Ki67 status were assessed by immunohistochemistry (IHC). Kaplan-Meier method and log-rank test were used to analyze PFS. RESULTS Of the 76 patients, 40 (52.6%) experienced dose reduction. Statistical analysis of the results revealed that there were no statistically significant differences observed between dose-reduced (16.5 months) vs non-dose reduced (17.7 months) patients in PFS (p=0.5493). For patients with Ki67 ≥ 14%, PFS was 15.2 months (95% CI: 10.2 to 22.2 months; p= 0.3024). In patients with PR ≥ 20%, median PFS was 25.0 months (lower 95% CI: 16.8 months; p=0.0069). CONCLUSION Our study indicated that dose reduction of palbociclib is frequently required but does not appear to affect PFS. PR expression was suggested to be a significant predictive factor for palbociclib responsiveness.