Gabriel Hortobagyi, MD, FACP, of the The University of Texas MD Anderson Cancer Center, Houston, TX, gives a summary of the findings of the MONALEESA-2 clinical trial (NCT01958021). The MONALEESA-2 study recruited 668 patients who were post-menopausal, had hormone receptor positive, HER2 negative advanced or metastatic breast cancer who had received no prior therapy for advanced disease. These patients were randomly assigned to either letrozole (a commonly used endocrine therapy) plus placebo, or letrozole plus ribociclib (a CDK46 inhibitor). Adverse events were commonly seen but were mostly uncomplicated changes and very few patients discontinued treatment on the basis of adverse events. The side effects were managed with dose interruptions and dose reductions. On the basis of the results, Dr Hortobagyi explains that it was concluded that patients who received ribociclib with letrozole had a statistically significant and a clinically meaningful increase in progression-free survival (PFS) compared with letrozole plus placebo. The treatment benefit was consistent across patient subgroups and for other secondary endpoints. He explains that in conclusion, this combination represents an important advance for patients with metastatic hormone receptor positive breast cancer. Recorded at the 2016 annual meeting of the European Society of Medical Oncology (ESMO), held in Copenhagen, Denmark.