On October 12, 2021, the U.S. Food and Drug Administration (FDA) approved abemaciclib (Verzenio®) with endocrine therapy (tamoxifen or an aromatase inhibitor) for adjuvant treatment of adult patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative, node-positive, early breast cancer at high risk for recurrence and a Ki-67 score ≥ 20%, as determined by an FDA-approved test. This is the first CDK4/6 inhibitor approved for adjuvant treatment of breast cancer.
FDA also approved the Ki-67 IHC MIB-1 pharmDx assay as a companion diagnostic for selecting patients for the indication.
Efficacy was evaluated in a randomized 1:1, open-label, two-cohort, multicenter trial (monarchE; NCT03155997) of adult patients with HR-positive, HER2-negative, node-positive, resected, early breast cancer with clinical and pathologic features consistent with a high risk for disease recurrence. Patients were randomized to receive either two years of abemaciclib plus their physician’s choice of standard endocrine therapy or standard endocrine therapy alone.
The major efficacy outcome measure was invasive disease-free survival (IDFS). In patients with high risk of recurrence and Ki-67 score ≥ 20% (n = 2,003), the trial demonstrated a statistically significant improvement in IDFS (HR = 0.626; 95% CI = 0.488, 0.803; p = 0.0042). IDFS at 36 months was 86.1% (95% CI = 82.8, 88.8) for patients receiving abemaciclib plus tamoxifen or an aromatase inhibitor and 79.0% (95% CI = 75.3, 82.3) for those receiving tamoxifen or an aromatase inhibitor. Overall survival data were not mature at the time of the IDFS analysis.
The most common adverse reactions in 20% or more of patients were diarrhea, infections, neutropenia, fatigue, leukopenia, nausea, anemia, and headache.
The recommended abemaciclib starting dose is 150 mg taken twice daily in combination with tamoxifen or an aromatase inhibitor for two years or until patients experience disease recurrence or unacceptable toxicity.
The review used the Real-Time Oncology Review pilot program, which streamlined data submission prior to the filing of the entire clinical application, and the Assessment Aid, a voluntary submission from the applicant to facilitate FDA’s assessment.
Healthcare professionals should report all serious adverse events they suspect are associated with the use of any medicine and device to FDA’s MedWatch Reporting System or by calling 800-FDA-1088.