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Later report from the monarchE trial registered as NCT03155997, in Annals of Oncology (2026); its title describes an updated or longer-term analysis.
Background: Adjuvant abemaciclib combined with endocrine therapy (ET) significantly improved invasive disease-free survival (IDFS) in patients with hormone receptor (HR)-positive, human epidermal growth factor 2 (HER2)-negative, node-positive, high-risk early breast cancer (EBC). The impact on overall survival (OS) remained unknown.
Patients and methods: In the phase III monarchE trial (NCT03155997), patients received ET for at least 5 years with or without abemaciclib for 2 years. In this article, we report the primary OS results, a key secondary endpoint, and updated estimates of IDFS and distant relapse-free survival (DRFS).
Results: Overall, 5637 patients underwent randomization, with 2808 assigned to abemaciclib-ET, and 2829 to ET. In the intent-to-treat population, with a median follow-up of 76.2 months, abemaciclib-ET resulted in a 15.8% lower risk of death than ET [661 deaths; hazard ratio 0.842, 95% confidence interval (CI) 0.722-0.981, P = 0.027], meeting the prespecified boundary for significance. The 7-year OS was 86.8% with abemaciclib-ET and 85.0% with ET (absolute difference, 1.8%). OS benefit was consistent across prespecified subgroups. In addition to patients who had already died of metastatic disease, fewer patients in the abemaciclib-ET arm were living with metastatic disease compared with the ET arm (6.4% versus 9.4%). Sustained improvement was demonstrated in IDFS and DRFS (hazard ratio 0.734, 95% CI 0.657-0.820 and hazard ratio 0.746, 95% CI 0.662-0.840, respectively). Seven-year IDFS was 77.4% with abemaciclib-ET and 70.9% with ET (absolute difference, 6.5%) and 7-year DRFS were 80.0% and 74.9% (absolute difference, 5.1%). The long-term safety data compiled did not support any concerns of delayed toxicities.
Conclusions: Adjuvant abemaciclib-ET resulted in a statistically significant and clinically meaningful improvement in OS compared with ET in patients with HR-positive, HER2-negative, node-positive, high-risk EBC. At 7 years, abemaciclib-ET continued to demonstrate a sustained IDFS and DRFS benefit.
Indexed on Europe PMC as PubMed record 41110697 (DOI 10.1016/j.annonc.2025.10.005). Its abstract cites the registry id NCT03155997, which is how it was matched to this trial; no figure has been checked by an editor.
A second publication from the monarchE trial, later than the first and described in its title as an update or longer-term analysis. Read it with the primary publication linked from the trial page; the record was linked automatically and its figures have not been checked by hand.
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