Adding ribociclib to standard endocrine therapy (ET) improves outcomes in patients with hormone receptor (HR)-positive, HER2-negative early breast cancer, according to research presented at the ASCO Annual Meeting 2023.

Ribociclib improved both invasive disease-free survival (iDFS) and distant disease-free survival (DDFS) when added to ET in the phase 3 NATALEE trial.

The trial (NCT03701334) included 5101 patients with stage II-III, HR-positive, HER2-negative breast cancer who had received up to 12 months of prior ET.

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Patients were randomly assigned to receive ribociclib plus ET (n=2549) or ET alone (n=2552). Ribociclib was given at 400 mg per day, 3 weeks on, 1 week off, for 3 years. ET consisted of letrozole or anastrozole for at least 5 years. Men and premenopausal women also received goserelin.

The 3-year iDFS rate was 90.4% in the ribociclib-ET arm and 87.1% in the ET-alone arm (hazard ratio [HR], 0.748; 95% CI, 0.618-0.906; P =.0014). The iDFS benefit seen with ribociclib was consistent across subgroups.

The 3-year DDFS rate was 90.8% in the ribociclib-ET arm and 88.6% in the ET-alone arm (HR, 0.739; 95% CI, 0.603-0.905; P =.0017).

Follow-up is ongoing for overall survival (OS), but there was a trend toward improved OS in the ribociclib-ET arm (HR, 0.759; 95% CI, 0.539-1.068; P =.0563).

Ribociclib was safe and well tolerated at the 400 mg dose, according to study presenter Dennis J. Slamon, MD, of the University of California, Los Angeles.

The most common adverse events (AEs) that led to treatment discontinuation were liver-related AEs (8.9% in the ribociclib arm and 0.1% in the ET-alone arm) and arthralgia (1.3% and 1.9%, respectively).

These results support ribociclib and ET as “a new treatment of choice” in a broad population of patients with stage II-III, HR-positive, HER2-negative early breast cancer at risk of recurrence, Dr Slamon said. 

Disclosures: This research was supported by Novartis. Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.

Slamon D, Stroyakovskiy D, Yardley DA, et al. Ribociclib and endocrine therapy as adjuvant treatment in patients with HR+/HER2− early breast cancer: Primary results from the phase III NATALEE trial. ASCO 2023. June 2-6, 2023. Abstract LBA500.