Results from a study presented at the European Society of Modern Oncology 2020 found that adding abemaciclib to hormonal therapy reduces the risk of cancer recurrence by 25% in patients with high-risk early hormone receptor (HR)-positive human epidermal growth factor receptor 2 (HER2)-negative breast cancer, according to a press release.

The phase 3 monarchE study included 5637 patients with HR-positive, HER2-negative early breast cancer with clinical and/or pathological risk factors putting them at high risk for relapse. After completing their primary treatment, patients were randomized on an open-label basis to abemaciclib (150 mg twice daily for 2 years) plus endocrine therapy or endocrine therapy alone.

The researchers found a 25% reduction in recurrence of cancer within the first 2 years when abemaciclib was added to hormone therapy compared with hormone therapy alone. Further, 11.3% of patients in the control group had a relapse of their cancer compared with 7.8% of those in the abemaciclib group, with an absolute difference of 3.5%, which translates to a 25.3% reduction in risk. Further, most of the reductions occurred in sites of distant metastases, especially to liver and bone.

“This is the first study to show that adding a CDK4/6 inhibitor to endocrine therapy significantly improves invasive disease-free survival in the adjuvant setting,” said Giuseppe Curigliano, MD, PhD, chair of the ESMO Guidelines Committee, in a press release. “This is a very important trial and the findings will change practice. Once approved for high risk HR-positive, HER2-negative early breast cancer the new standard of care for these patients will be to add 2 years of abemaciclib to endocrine therapy.”

A total of 463 patients discontinued abemaciclib due to adverse events, most commonly diarrhea, with 306 of these continued on endocrine therapy. Additionally, the protocol allowed dose reduction from 150 to 100 mg twice daily if required.  

“Adherence to treatment will be an important issue to be considered in the real-life population of patients when this treatment is approved and used in clinical practice,” Curigliano said in a press release.

Curigliano suggested that including genetic signature into the assessment of patients at high risk, in addition to the number of positive lymph nodes, tumor size, histologic grade, and Ki-67 would have made the study more interesting. He also suggested that future studies should focus on whether researchers can potentially spare chemotherapy in the group of patients treated with a CDK4/6 inhibitor.

REFERENCE
First new drug in years reduces recurrence in high-risk hormone receptor positive early breast cancer. ESMO 2020. https://www.esmo.org/newsroom/press-office/esmo2020-breast-cancer-monarche-abemaciclib. Published September 20, 2020. Accessed September 21, 2020.