The FDA approved the combination of abemaciclib and either tamoxifen or an aromatase inhibitor for adjuvant treatment for some adults with HR-positive HER2-negative, node-positive, early breast cancer, according to a press release. 

The approval is for patients with a high risk of recurrence and a Ki-67 score of ≥20%. As part of the designation, the FDA approved the Ki-67 IHC MIB-1 pharmDx assay as a companion diagnostic. 

The approval was based on results from the monarchE trial, which randomized patients to either two years of abemaciclib and endocrine therapy or endocrine therapy alone. The major efficacy outcome of the trial was invasive disease-free survival (IDFS).

Results from the trial showed patients with a high risk of recurrence and Ki-67 score ≥20% had a statistically significant improvement in the IDFS (HR = 0.626; 95% CI, 0.488-0.803; P = 0.0042). The IDFS at 36 months was 86.1% (95% CI: 75.3-82.3) for patients receiving tamoxifen or an aromatase inhibitor. The results for overall survival were not mature at the time of analysis.

In reviewing the safety of the treatment, the FDA noted that the most common adverse reactions included diarrhea, infections, and neutropenia.