Dr West on Adjuvant Endocrine Therapy Plus a CDK4/6 Inhibitor in Early-Stage Breast Cancer

Malinda West, MD, MS, assistant professor, Division of Hematology, Oncology and Palliative Care, Department of Medicine, University of Wisconsin Carbone Cancer Center, School of Medicine and Public Health, discusses the use of adjuvant endocrine therapy in combination with CDK4/6 inhibitors in the treatment of patients with early-stage HER2-negative breast cancer.

The phase 3 monarchE trial (NCT03155997) investigated the use of endocrine therapy with or without adjuvant abemaciclib (Verzenio), a CDK4/6 inhibitor, following surgery in patients with hormone receptor (HR)–positive, HER2-negative, node-positive, high-risk, early breast cancer. Abemiciclib was given as an adjuvant treatment for 2 years in combination with up to 10 years of endocrine therapy, West begins. This randomized, open-label study was one of the first success stories to have evaluated the use of adjuvant therapy in combination with CDK4/6 inhibitors within this treatment arena, West says. The findings from this trial led to the March 2023 FDA approval of abemiciclib in combination with endocrine therapy for the adjuvant treatment of adult patients with HR-positive/HER2-negative, node-positive, early breast cancer that is at a high risk of recurrence, West explains.

Moreover, treatment with the monarchE approach of abemaciclib and endocrine therapy led to significant benefits in terms of invasive disease-free survival and distant relapse-free survival vs standard endocrine therapy alone, West emphasizes. Additionally, the phase 3 NATALEE trial (NCT03701334) is investigating another CDK4/6 inhibitor, ribociclib, (Kisqali) with endocrine therapy as adjuvant treatment in patients with HR-positive/HER2-negative early breast cancer, West notes. Despite differences between these trials, both have produced encouraging data showing that CDK4/6 inhibitors reduce the risk of recurrence in this patient population, West expands.

Overall, both phase 3 trials were conducted in hopes of addressing unmet needs in patients with early-stage breast cancer who are at risk for late and distant relapses, she continues, noting that even patients with node-negative disease or disease with 1 to 3 positive lymph nodes have a significant risk for disease recurrence after endocrine therapy alone. For this reason, adjuvant endocrine therapy plus CDK4/6 inhibitors continues to be evaluated in patients with HR-positive/HER2-negative disease, West concludes.