Updated monarchE data show continued abemaciclib benefit
medwireNews: Further follow-up of the monarchE trial shows that the addition of abemaciclib to adjuvant endocrine therapy continues to offer an invasive disease-free survival (IDFS) benefit to patients with high-risk, hormone receptor (HR)-positive, HER2-negative, early breast cancer.
Reporting the findings of the primary outcome analysis at the 2020 San Antonio Breast Cancer Symposium, Priya Rastogi (University of Pittsburgh, Pennsylvania, USA) noted that the combination of the CDK4/6 inhibitor and endocrine therapy was associated with a significant 28.7% reduction in the risk for invasive disease versus endocrine therapy alone after a median follow-up of 19 months.
These results follow on from the interim analysis, conducted at a median follow-up of 15.5 months and previously reported by medwireNews, which showed a significant risk reduction of 25.3%.
Ruth O'Regan comments on the monarchE, PENELOPE-B and PALLAS trials (6:35)
The phase 3 trial enrolled patients with nonmetastatic high-risk disease, defined as the presence of at least four positive nodes or 1–3 nodes and either grade 3 disease, tumor size of at least 5 cm, or centrally assessed Ki-67 levels of 20% or greater.
In the current report, the 2-year IDFS rate was 92.3% for the 2808 participants who received abemaciclib 150 mg twice a day for up to 2 years alongside standard endocrine therapy, compared with 89.3% for their 2829 counterparts who received just endocrine therapy.
This equated to a “clinically meaningful” absolute improvement in IDFS of 3.0 percentage points with the addition of the CDK4/6 inhibitor, said Rastogi.
The abemaciclib group also had significantly better distant relapse-free survival than the control group, with 2-year rates of 93.8% and 90.8%, respectively, and a decrease in the relapse risk of 31.3%.
Rastogi also reported on the 2498 trial participants with high Ki-67 levels (≥20%), noting that abemaciclib addition achieved a significant 30.9% reduction in the risk for invasive disease relative to endocrine therapy alone. The 2-year IDFS rates were 91.6% and 87.1%, respectively.
“These results may mark a notable treatment advance in the last two decades for people living with high-risk, node-positive, HR-positive, HER2-negative early breast cancer,” and have the potential to change how this patient population is treated, she commented in a press release.
The presenter pointed out, however, that the “study is ongoing, until the final assessment of overall survival.”
Commenting on the findings in a press conference, C Kent Osborne (Baylor College of Medicine, Houston, Texas, USA) said that “these results are very encouraging, especially in the subgroup of tumors with high proliferation.”
But he noted that “caution in the interpretation is needed, given the still rather short follow-up, given that [HR]-positive disease is known for its persistent recurrence rate even past 10 years, and given that this class of inhibitors is largely cytostatic rather than cytocidal.”
Osborne continued: “With these caveats in mind, this is still an extremely important trial that could be practice changing in this very high-risk patient population […] if the results continue to be positive and show improved overall survival with longer follow-up.”
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