Final overall survival (OS) results from the MONARCH 2 and MONALEESA-3 trials show consistent OS benefits with the cyclin-dependent kinase 4/6(CDK4/6) inhibitors abemaciclib (Verzenio, Lilly) and ribociclib (Kisqali, Novartis). The new data establish the foundation for adding these drugs to endocrine therapy in the treatment of patients with hormone receptor positive, human epidermal receptor negative (HR+/HER2-) advanced breast cancer (ABC). The new results were presented  at the European Society of Medical Oncology (ESMO) 2019 Annual Meeting and were published online September 29 in JAMA Oncology. The results from MONARCH 2 show that after a median follow-up of approximately 4 years (47.7 months), patients with HR+/HER- ABC lived significantly longer with the combination of abemaciclib and fulvestrant. Median OS was 46.7 months with the combination and 37.3 months with fulvestrant alone (hazard ratio [HR], 0.757; 95% confidence interval [CI], 0.606 – 0.945; P = .0137).

A similar benefit was seen with the combination of ribociclib and fulvestrant in MONALEESA-3. After a median follow-up of 39.4 months, median OS was not reached with the combination of ribociclib and fulvestrant; it was 40.0 months for patients who received fulvestrant alone (HR, 0.724; 95% CI, 0.568 – 0.924; P = .00455).