The addition of two years of abemaciclib therapy to adjuvant hormone therapy decreases the likelihood of recurrence in patients with RH-positive/HER2-negative localized breast cancer at high risk of relapse, as demonstrated by the MONARCHe clinical study, published in Journal of Clinical Oncology, whose authors include Dr. Javier Cortés, director of the International Breast Cancer Center (IBCC).
Luminal breast cancer, which has hormone receptor expression (RH-positive/HER2-negative), is the most common subtype of breast cancer, accounting for about 70% of all diagnosed cases.
Hormonal treatment is an essential part of the complementary treatment of these tumours. However, in spite of this and of the use of adjuvant chemotherapy, a significant percentage of patients continue to have a recurrence of the disease.
Inhibitors (abemaciclib, palbociclib, and ribociclib) of CDK4/CDK6, proteins critical to the growth of breast tumour cells, have demonstrated very significant antitumour activity in patients with RH-positive/HER2-negative metastatic breast cancer. For this reason, all three agents are now approved in combination with hormonal treatment for patients with advanced HR-positive/HER2-negative breast cancer, both in first-line treatment and after progression to hormonal treatment.
This phase III clinical trial was conducted in 603 centres in 38 countries, and included 5,637 patients with RH-positive/HER2-negative early breast cancer with a high risk of relapse, defined mainly by the presence of locoregional lymph-node involvement. Patients were randomly selected to receive adjuvant hormone therapy with abemaciclib (2,808 patients) or without abemaciclib (2,829 patients). The primary endpoint of the study was invasive-disease-free survival.
This interim analysis of the study demonstrates that treatment with abemaciclib significantly reduces the risk of invasive recurrence or death by 25%, compared to exclusive adjuvant hormonal treatment. These findings have become more relevant since palbociclib, another CDK4/CDK6 inhibitor, was unable to demonstrate its efficacy in the same context in the PALLAS phase III clinical study.
Based on the results of this study, regulatory agencies are evaluating the authorization of adjuvant therapy with abemaciclib for the treatment of this group of patients.