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The FDA approved the CDK4/6 inhibitor abemaciclib (Verzenio), in combination with standard adjuvant endocrine therapy, for certain patients with early breast cancer who are at high risk of recurrence, .

Indicated for patients who are node-positive and have hormone receptor-positive/HER2-negative disease, eligibility for the combination further requires a score of ≥20% on the cellular proliferation marker Ki-67, as determined by an FDA-approved test.

Abemaciclib is the first CDK4/6 inhibitor approved in this setting, according to Lilly's news release. Approval was based on results from a subgroup analysis of the phase III monarchE trial.

"The design and results of the monarchE study are practice-changing and represent the first advancement in adjuvant treatment of [hormone receptor-positive/HER2-negative] breast cancer in a very long time," investigator Sara M. Tolaney, MD, MPH, of Dana-Farber Cancer Institute in Boston, said in a statement.

"This FDA approval for Verzenio in combination with endocrine therapy in the early breast cancer setting has the potential to become a new standard of care for this population," she continued. "We are encouraged by the marked reduction in the risk of recurrence even beyond the 2-year treatment period in these patients, and I'm grateful to be able to offer this as a treatment option to my patients."

In monarchE, patients were randomized to receive 2 years of abemaciclib (150 mg twice daily) plus physician's choice of standard endocrine therapy (tamoxifen or an aromatase inhibitor) versus endocrine therapy alone. Patients in both treatment arms continued to receive adjuvant endocrine therapy for up to 5 to 10 years, as recommended by their clinician.

The study's primary endpoint was invasive disease-free survival (iDFS), which was met in an interim analysis with a statistically significant improvement observed in the abemaciclib arm. The subgroup analysis (n=2,003) included patients with at least four positive axillary lymph nodes or one to three positive nodes with either grade 3 disease and/or tumor size ≥5 cm, and whose tumors had a Ki-67 score of 20% or higher.

In a post-hoc analysis with additional follow-up, there were 104 events in the abemaciclib arm versus 158 in the control arm, representing a 37% decreased risk of breast cancer recurrence or death with the addition of abemaciclib (HR 0.626, 95% CI 0.49-0.80) and an absolute benefit in iDFS of 7.1% at 3 years.

The most common adverse reactions reported in the abemaciclib group were diarrhea, infections, fatigue, nausea, headache, vomiting, stomatitis, decreased appetite, dizziness, rash, and alopecia. The most common laboratory abnormalities were increases in creatinine, alanine transaminase, and aspartate aminotransferase; decreases in white blood cell counts, neutrophils, lymphocytes, and platelets; and hypokalemia and anemia.

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