Benefits of Adjuvant Abemaciclib for Breast Cancer Sustained Beyond Treatment

Adjuvant abemaciclib reduces the risk for disease recurrence in patients with hormone receptor-positive,
human epidermal growth factor receptor 2 (HER2)-negative, node-positive, high-risk, early breast cancer,
according to the results of a study published in The Lancet Oncology.

Stephen RD Johnston, MD, PhD, and colleagues presented updated results from an interim analysis of the
phase 3, open-label, randomized monarchE trial to examine overall survival as well as invasive
disease-free survival (DFS) and distant relapse-free survival. “The benefit is sustained beyond the
completion of treatment with an absolute increase at 4 years, further supporting the use of abemaciclib
in patients with high-risk hormone receptor-positive, HER2-negative early breast cancer,” the study
authors wrote.

The study group consisted of adult patients who had hormone receptor-positive, HER2-negative,
node-positive early breast cancer at a high risk of recurrence. Patients were randomly assigned 1:1 and
stratified by menopausal status, previous chemotherapy, and region to receive standard-of-care endocrine
therapy of physician’s choice for up to 10 years with or without abemaciclib 150 mg orally twice a day
for 2 years (defined as the treatment period).

Median Invasive DFS Not Reached at 42 Months

Cohort 1 included patients with high-risk disease, defined as either four or more positive axillary lymph
nodes, or between one and three positive axillary lymph nodes and either grade 3 disease or tumor size of
5 cm or larger. Cohort 2 consisted of a smaller group of patients who presented with between one and three
positive axillary lymph nodes and Ki-67 levels of at least 20% as an additional risk factor.

A total of 5,637 patients were randomly assigned (99.4% women; 0.6% men); 2,808 received abemaciclib plus
endocrine therapy and 2,829 received endocrine therapy alone. In both groups, median invasive DFS was not
reached at a median follow-up of 42 months (interquartile range, 37-47), and the previously reported
invasive DFS benefit was sustained (HR, 0.664 [95% CI, 0.578-0.762; nominal P<0.0001]).

The absolute difference in invasive DFS between the groups at 4 years was 6.4% (85.8% [95% CI, 84.2-87.3]
in the abemaciclib plus endocrine therapy group vs 79.4% [95% CI, 77.5-81.1] in the endocrine therapy
alone group). In the abemaciclib plus endocrine therapy group, 5.6% of 2,808 patients died compared with
6.1% of 2,829 patients in the endocrine therapy alone group (HR, 0.929; 95% CI, 0.748-1.153).

Neutropenia Was Most Common Grade 3-4 Adverse Event

Neutropenia was the most common grade 3-4 adverse event, reported in 19.6% of patients receiving abemaciclib
plus endocrine therapy versus 0.9% of patients in the endocrine therapy alone group, followed by leukopenia (11.4% vs 0.4%) and diarrhea (7.8%
vs 0.2%). Serious adverse events occurred in 15.5% of patients receiving abemaciclib plus endocrine therapy
versus 9.1% of those receiving endocrine therapy alone. In the abemaciclib plus endocrine therapy group,
there were two treatment-related deaths due to diarrhea and pneumonitis but none in the endocrine therapy
alone group.

“Further follow-up is needed to establish whether overall survival can be improved with abemaciclib plus
endocrine therapy in these patients,” the study authors wrote.

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