FDA Approves Companion Diagnostic For Adjuvant Abemaciclib in High-Risk Early Breast Cancer


The FDA has given the Ki-67 IHC MIB-1 pharmDx assay a companion diagnostic approval for detecting Ki-67 expression in patients with high-risk early breast cancer who are being considered for treatment with abemaciclib.

Ki-67 IHC MIB-1 pharmDx has been approved by the FDA as a companion diagnostic for detecting Ki-67 expression in patients with high-risk breast cancer who may be eligible for treatment with abemaciclib (Verzenio) plus endocrine therapy, according to a press release from developer Agilent Technologies.1

The indication marks the first approval of an immunohistochemistry assay that measures Ki-67 expression in the context of treatment with abemaciclib.

“Agilent’s Ki-67 IHC MIB-1 pharmDx (Dako Omnis) companion diagnostic assay for the Dako Omnis advanced staining platform has been designed and tested to aid in evaluating risk of recurrence in early breast cancer (EBC),” Sam Raha, president of Agilent’s Diagnostics and Genomics Group, said in a press release. “Its approval establishes a clinically relevant standard for recurrence risk assessment in EBC so that more high-risk patients who may experience clinical benefit from treatment with Verzenio are identified.”

Experts expressed that understanding the risk of recurrence present in patients with early breast cancer is imperative in informing disease management and identifying those who are at high risk to inform treatment decisions and improve outcomes. Current methods for determining risk of recurrence in this patient population are based on staging and are performed according to standard clinical and pathologic disease features. Notably, experts indicated that these features may not capture the full risk of recurrence in those with early breast cancer.

Adjuvant abemaciclib was approved by the FDA on October 13, 2021 for patients with hormone receptor (HR)–positive, HER2-negative, node-positive early breast cancerwho are at high risk of recurrence with a Ki-67 score of 20% or greater.2 The designation was supported by findings from the phase 3 monarchE trial (NCT03155997)in which patients with HR-positive, HER2-negaitve early breast cancer who exhibited clinical and pathological features associated with a high risk of recurrence were randomized to receive either 150 mg of abemaciclib twice per day plus endocrine therapy or endocrine therapy alone.

Treatment with the experimental regimen resulted in a statistically significant improvement in invasive disease-free survival that translated to a 37% reduction in risk of disease recurrence or death (HR, 0.643; 95% CI, 0.475-0.872; P = .0042).

“The design and results of the monarchE study are practice-changing and represent the first advancement in adjuvant treatment of [HR-positive, HER2-negative] breast cancer in a very long time,” Sara M. Tolaney, MD, MPH, chief of the Division of Breast Oncology and associate director of the Susan F. Smith Center for Women's Cancers Senior Physician, Dana-Farber Cancer Institute, as well as an associate professor of medicine at Harvard Medical School, and investigator on the monarchE study, said in a press release.

“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. 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.”


  1. Agilent receives FDA companion ciagnostic approval for Ki-67 IHC MIB-1 pharmDx in high-risk early breast cancer. News release. Agilent Technologies. October 13, 2021. Accessed October 15, 2021. https://bwnews.pr/3n0zgQz
  2. FDA Approves Verzenio (abemaciclib) as the First and Only CDK4/6 Inhibitor for Certain People with HR+ HER2- High Risk Early Breast Cancer. Eli Lilly and Company. News release. October 13, 2021. Accessed October 13, 2021. https://bit.ly/3DFt5I7
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