Systematic review and meta-analysis of post-progression outcomes in ER+/HER2- metastatic breast cancer after treatment with endocrine therapy and CDK 4/6 inhibitors within randomized clinical trials.

Abstract

1059 Background: CDK4/6 inhibitors combined with endocrine therapy (ET) deeply transformed the treatment landscape of HR+/HER2− advanced breast cancer. After progression with the combination, there are no established guidelines for an optimal sequencing of the various therapeutic options. Data from randomized clinical trials (RCT) suggest that subsequent progression free survival (PFS2) was not compromised by the use of these drugs and time to subsequent chemotherapy (TTC) may be delayed. Therefore, we performed a meta-analysis to evaluate the benefit of such treatments on PFS2 and on delaying the TTC. Methods: We conducted a systematic literature search using PubMed to select all available randomized clinical trials of CDK4/6-inhibitors and ET reporting PFS2 or TTC data in first- or second-line therapy of HR+/HER2- pre- or postmenopausal metastatic breast cancer. We also reviewed abstracts and presentations from all major conference proceedings. We calculated the pooled hazard ratios (HR) for PFS2 and TTC with 95% confidence intervals (CI) using fixed-effects models. The pooled HRs for PFS and OS were also calculated. I2 was used to quantify heterogeneity between studies’ results. Results: Seven studies (PALOMA 1-2-3, MONALEESA 3-7, MONARCH 2-3) were included in our analyses (n = 3912 patients). A clear PFS2 benefit was observed in patients who received CDK 4/6 inhibitors + ET (pooled HR = 0.67, 95% CI = 0.61 to 0.74, I2 = 0.0%) and also a delay in subsequent TTC (pooled HR = 0.63, 95% CI = 0.58 to 0.70, I2 = 0.0%). As previously reported, the benefit in terms of PFS (pooled HR = 0.54, 95% CI = 0.50 to 0.59, I2= 0%) and OS (pooled HR = 0.77, 95% CI = 0.68 to 0.86, I2= 0%) was also confirmed. Conclusions: CDK4/6-inhibitors plus ET compared with ET alone improve PFS2, and TTC. The delay of chemotherapy can spare the patients toxicities, potentially improving the quality of life. Thus, the observed benefit in PFS2 may postpone the onset of endocrine resistance and may offer an additional therapeutic advantage in this setting.