New efficacy and safety data from the monarchE study show that chemotherapy administered before treatment with abemaciclib and estrogen therapy, led to a clinically meaningful improvement in invasive disease-free survival and distant relapse-free survival for women with HR-positive, ERBB2-negative, node-positive, early breast cancer at high risk of recurrence.
The study was published earlier this year in.
Neoadjuvant chemotherapy is often provided to such patients in hopes of achieving breast-conserving surgery. Although pathologic complete response rates can be higher than 50% after chemotherapy treatment in triple-negative and ERBB2-positive breast cancer, most patients with HR-positive and ERBB2-negative breast cancer have residual tumor at surgery after neoadjuvant chemotherapy, which is associated with an increased risk of recurrence.
“To our knowledge, abemaciclib is the first agent added to standard adjuvant estrogen therapy that has been shown to reduce the risk of recurrence in patients with HR-positive, ERBB2-negative early breast cancer with residual disease after neoadjuvant chemotherapy,” wrote the authors, who were led by Miguel Martin, MD, PhD, Hospital General Universitario Gregorio Marañon, Spain.
In 2021, Ffor the treatment of HR-positive/ERBB2-negative, node-positive, high-risk early breast cancer. Their decision was based on data from the
The study is at odds with the previously published, which found no benefit from treatment with the CDK4/6 inhibitor palbociclib (Ibrance, Pfizer) after 42.8 months of follow-up. The authors suggest that the disparate outcomes may be due to pharmacological differences between the two drugs as well as different dosing schedules: In monarchE, patients received abemaciclib on a continuous basis, while patients in Penelope-B received palbociclib for 21 days, followed by 7 days off. The treatment duration was 2 years in monarchE and 1 year in Penelope-B. Abemaciclib can be dosed continuously because it is a stronger inhibitor of CDK4 versus CDK6 compared to abemaciclib, and in vitro studies suggest that continuous dosing could be a key factor in creating profound inhibition of DNA synthesis.
The monarchE study included 5,637 patients who were randomized to receive standard of care estrogen therapy for 5 years with or without abemaciclib (150 mg, twice per day) for 2 years; 36.5% received abemaciclib. The mean age was 49.9 years; 70.8% were White, 22.8% Asian, and 2.7% Black.
The abemaciclib group had a clinically and statistically significant benefit in invasive disease-free survival (IDFS) (hazard ratio, 0.61; nominal P < .001) and distant relapse-free survival (DRFS) (HR, 0.61; nominal P < .001). At 2 years, DRFS was 89.5% in the abemaciclib group and 82.8% in the estrogen therapy–only group. IDFS was 87.2% and 80.6%, respectively. Patients who underwent neoadjuvant chemotherapy had a similar safety profile to the estrogen therapy–only group, although there was a higher incidence of treatment-emergent adverse events. The most common were diarrhea, infections, neutropenia, and fatigue. The most frequent grade treatment-emergent adverse events (of at least 3) were neutropenia and leucopenia.
The researchers noted that patients who underwent neoadjuvant chemotherapy had a worse prognosis than the intent-to-treat arm, as evidenced by a higher risk of 2-year recurrence (19% versus 11%). Exploratory subgroup analyses revealed that treatment with abemaciclib and estrogen therapy conferred IDFS and DRFS benefits regardless of the pathological tumor size and number of positive axillary lymph nodes.
The study was limited by the fact that it was open label, and the subgroup analyses were not powered to find statistically significant associations.
Dr. Martin has received grants from Eli Lilly, which funded monarchE.