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First-line abemaciclib and endocrine therapy
Source: Breast Cancer Treatment (PDQ®)–Health Professional Version, National Cancer Institute.
Source updated: April 25, 2025 · Captured 2026-09-09.
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Abemaciclib, another CDK4/6 inhibitor, has also been tested in the first-line setting for postmenopausal patients with HER2-negative hormone receptor–positive, recurrent or metastatic breast cancer.
Evidence (first-line abemaciclib and endocrine therapy):
MONARCH 3 (NCT02246621) was a randomized, double-blind, phase III trial that evaluated first-line abemaciclib or placebo plus a nonsteroidal AI in 493 postmenopausal women with HER2-negative hormone receptor–positive, advanced breast cancer.[19]
MONARCH 3 (NCT02246621) was a randomized, double-blind, phase III trial that evaluated first-line abemaciclib or placebo plus a nonsteroidal AI in 493 postmenopausal women with HER2-negative hormone receptor–positive, advanced breast cancer.[19]
The primary end point, investigator-assessed PFS, was met. After a median follow-up of 17.8 months, the PFS was not reached in the abemaciclib arm and was reached at 14.7 months in the placebo arm (HR, 0.54; 95% CI, 0.41–0.72; P = .000021).
MONARCH 3 (NCT02246621) was a randomized, double-blind, phase III trial that evaluated first-line abemaciclib or placebo plus a nonsteroidal AI in 493 postmenopausal women with HER2-negative hormone receptor–positive, advanced breast cancer.[19]
In the final analysis of OS, there was a nonsignificant difference in median survival (median OS, 66.8 months [abemaciclib arm] vs. 53.7 months [placebo arm]; HR, 0.804; 95% CI, 0.637–1.015; P = .066).[20][Level of evidence B1]
Source links and citations
MONARCH 3 (NCT02246621) was a randomized, double-blind, phase III trial that evaluated first-line abemaciclib or placebo plus a nonsteroidal AI in 493 postmenopausal women with HER2-negative hormone receptor–positive, advanced breast cancer.[19]
The side effect profile of abemaciclib differs from the other CDK4/6 inhibitors. Diarrhea was the most frequent adverse event in the abemaciclib arm, although most of the diarrhea cases were grade 1.
MONARCH 3 (NCT02246621) was a randomized, double-blind, phase III trial that evaluated first-line abemaciclib or placebo plus a nonsteroidal AI in 493 postmenopausal women with HER2-negative hormone receptor–positive, advanced breast cancer.[19]
Neutropenia was more common in the abemaciclib arm; however, only 21.1% of participants experienced grade 3 to 4 neutropenia.
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Preserved source evidence · Not medical advice