A CDK 4/6 Inhibitor Shows an Overall Survival Benefit in Stage 4 Breast Cancer for the First Time

In hormone-positive, metastatic (stage 4) breast cancer, previous studies had established the importance of CDK 4/6 inhibitors. Acting on the cell’s mitotic division cycle, these CDK 4/6 inhibitor drugs protect hormonal therapies against resistance developing. Previous studies, particularly in premenopausal patients with breast cancer, showed that using these drugs after multiple lines of treatment improved disease-free survival, but had not demonstrated a contribution to "overall survival".

For the first time , one CDK4/6 inhibitor used in first-line (initial) treatment— ribociclib (Kisqali) —was shown to improve overall survival in patients with breast cancer who had not entered menopause. These landmark results from MONALEESA-7 were presented at the American Society of Clinical Oncology (ASCO) 2019 Congress.

Study Summary

• The study enrolled 672 previously untreated premenopausal patients with metastatic, hormone-positive breast cancer.
• All patients received GnRH drugs to suppress ovarian function and induce menopause.
• Patients took tamoxifen, letrozole or anastrozole as endocrine therapy.
• The experimental group received ribociclib in addition to these treatments, while the control group received placebo.
• After an average follow-up of 35 months, ribociclib was shown to provide an additional 11 months of progression-free survival (time until disease worsens).
• At month 42, 70% of patients taking ribociclib were alive, and ribociclib was shown to contribute a 24% improvement in overall survival.
• No new unmanageable side effects were encountered during follow-up.

Genetic analysis of DNA from blood samples obtained from study patients is currently ongoing. The aim is to identify patients who benefit most from ribociclib, allowing us to predict from the outset for which patients this agent will be more effective.

Commentary

This study indicated that CDK4/6 inhibitors can be used safely in premenopausal patients with breast cancer. Oncology leaders described the study results as groundbreaking . We believe that studies in premenopausal patients involving the other CDK4/6 inhibitors, palbociclib (Ibrance) and abemaciclib (Verzenio), will also conclude soon. We will continue to follow new studies in this field for you.