Meta-analysis of CDK4/6 inhibitor rechallenge shows improved progression-free survival in advanced breast cancer

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Breast cancer research : BCR Published May 28, 2026 Medically reviewed May 28, 2026 Study authors: Veta Darkovski Jasmina, Michelon Isabella, Gazzoni Gabriela, Mamede Isadora, Jeong Yujin, Cavalcante… PubMed ↗ DOI ↗ By Dr. Julia Lee, PhD · Oncology, Genomics & Drug Development

Key Takeaway

Consider CDK4/6 inhibitor rechallenge for progression on endocrine therapy alone in advanced breast cancer.

This meta-analysis synthesizes evidence from phase II and III clinical trials focusing on CDK4/6 inhibitors, specifically abemaciclib, palbociclib, and ribociclib, in patients with hormone receptor-positive, HER2-negative advanced or metastatic breast cancer. The study compares CDK4/6 inhibitor rechallenge plus endocrine therapy against endocrine therapy alone. The primary outcome assessed was progression-free survival, with overall survival as a secondary outcome.

The analysis found that rechallenge plus endocrine therapy resulted in a progression-free survival of 5.8 months compared to 3.7 months with endocrine therapy alone. This corresponds to a hazard ratio of 0.71 with a 95% CI of 0.63-0.81 and a P value less than 0.001, representing a 29% reduction in the risk of progression or death. No overall survival benefit was observed, with a hazard ratio of 1.04 and a 95% CI of 0.70-1.55.

Subgroup analyses suggested greater benefit when switching to a different CDK4/6 inhibitor, showing a hazard ratio of 0.61 with a 95% CI of 0.52-0.72. Among the specific agents, abemaciclib demonstrated the longest progression-free survival at 7.9 months versus 4.6 months for palbociclib and 5.5 months for ribociclib. Progression-free survival was 5.3 months for patients with ESR1 alterations and 4.7 months for those with PIK3CA alterations. Safety data and tolerability were not reported in this synthesis.

Study Details

Study typeMeta analysis

Sample sizen = 1,396

EvidenceLevel 1

PublishedMay 2026

PMID42192452

View Original Abstract ↓

BACKGROUND: Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) combined with endocrine therapy (ET) are the standard of care for hormone receptor (HR)-positive, HER2-negative advanced/metastatic breast cancer (BC). However, the optimal strategy after progression remains uncertain. METHODS: PubMed, Cochrane, and Embase databases were searched in April 2025 for phase II/III clinical trials evaluating CDK4/6i rechallenge in advanced breast cancer. We evaluated progression-free survival (PFS) and overall survival (OS) using Cox proportional hazards models, reporting hazard ratios (HRs) with 95% confidence intervals (CIs). Analyses were conducted on R (v.4.2.2). RESULTS: Eight trials including 1396 patients were included, of whom 839 received CDK4/6i rechallenge plus ET, and 557 received ET alone. Median PFS was 5.8 months vs 3.7 months, with a 29% reduction in risk of progression or death (HR 0.71; 95% CI 0.63-0.81; P < 0.001). No OS benefit was observed (HR 1.04; 95% CI 0.70-1.55). Switching to a different CDK4/6i appears to confer greater benefit (HR 0.61; 95% CI 0.52-0.72), yet most patients who switched CDK4/6i received abemaciclib, which was associated with the longest PFS (7.9 months) compared with palbociclib (4.6 months) or ribociclib (5.5 months). Patients harboring ESR1 or PIK3CA alterations demonstrated a median PFS of 5.3 (3.6-7.4) and 4.7 (3.6-6.7) months, respectively. CONCLUSIONS: This meta-analysis suggests that CDK4/6 inhibitor rechallenge post-progression offers additional benefit to ET alone.