Abraheem, Ahmed

e13167 Background: Abemaciclib represents a significant therapeutic advancement in the treatment of advanced metastatic breast cancer. As a selective protein-dependant kinase 4 and 6 (CDK4/6) inhibitor, it acts as a growth blocker. This study aims to evaluate the efficacy and safety of abemaciclib in combination with endocrine therapy for patients with metastatic breast cancer. Methods: We conducted an electronic search on December 27, 2024 using PubMed, Scopus, and the Cochrane database. Our inclusion criteria involved only randomized clinical trials evaluating the efficacy and safety of abemaciclib in combination to endocrine therapy in advanced breast cancer. Our primary outcomes were progression-free survival, overall response rate, overall survival, and grade 3 or 4 adverse effects. The hazard, odds, and risk ratios with 95% confidence intervals were used to determine the effect size. A random-effects model was applied. Results: Out of the 1,648 articles screened, only seven papers from five clinical trials met our inclusion criteria, comprising a total of 2,362 patients. Progression-free survival was significantly improved with abemaciclib in combination with endocrine therapy compared to endocrine therapy alone (hazard ratio: 0.58; 95% CI: 0.51–0.65; p < 0.001). Moreover, abemaciclib improved overall survival (hazard ratio: 0.78; 95% CI: 0.66–0.91; p = 0.002). Additionally, the overall response rate was higher with abemaciclib plus endocrine therapy compared to endocrine therapy alone (odds ratio: 2.75; 95% CI: 1.98–3.80; p < 0.001). However, grade three or higher adverse events were significantly more common in the abemaciclib group (risk ratio: 2.62; 95% CI: 2.30–2.99; p < 0.001). Conclusions: Abemaciclib combined with endocrine therapy is an effective treatment option for patients with HR-positive, HER2- negative advanced breast cancer. This combination significantly improves progression-free survival, overall survival, and response rate, making it a valuable therapeutic option in breast cancer. However, higher adverse events were observed in the abemaciclib group.