Abemaciclib as adjuvant treatment for high-risk early breast cancer

To adapt the GHEMA report of abemaciclib, an inhibitor of cyclin-dependent kinases 4 and 6. European Medicines Agency authorization (April 2022) includes, in combination with endocrine therapy, the adjuvant treatment of adult patients with hormone receptor positive, human epidermal growth factor receptor 2 negative, node-positive, early breast cancer at high risk of recurrence.

The efficacy and safety of abemaciclib were evaluated in a randomized, open-label, and multicenter phase III study. A total of 5637 patients diagnosed with early breast cancer with hormone receptor positive, human epidermal growth factor receptor 2 negative, node positive, and high risk of recurrence were included. High risk was defined as patients with 4 or more positive axillary lymph nodes, or 1-3 positive axillary lymph nodes and at least one of the following: tumor size ≥5 cm, histologic grade 3, or Ki-67≥20%. Patients were randomized (1:1) to receive adjuvant abemaciclib+endocrine therapy (n = 2808) or endocrine therapy alone (n = 2829) for 2 years, with endocrine therapy prescribed for at least 5 years.

With a median follow-up of 15.5 months, abemaciclib+endocrine therapy demonstrated a statistically significant improvement in invasive disease-free survival versus endocrine therapy alone [HR = 0.747 (95% CI 0.598-0.932), P = 0.0096]; achieving an absolute improvement of 3.5% invasive disease-free survival rate at 2-years. These results were maintained, with a median follow-up of 27.7 months: absolute improvement of 2.7% and 5.4% in invasive disease-free survival rate at 2 and 3 years, respectively. All-causality grade 3 or 4 adverse events were 45.9% for abemaciclib and 12.9% for endocrine therapy, and included neutropenia (19.6% vs. 0.8%), leukopenia (11.4% vs. 0.4%), and diarrhea (7.8% vs. 0.2%).

The results of the pivotal trial are sufficient to consider abemaciclib as adjuvant treatment for high-risk early breast cancer in highly selected patients. However, in order to the efficacy results present less uncertainty, we must wait for a evaluation later, in which we can have a mature determination at 3 years (with more patients at risk).