MADRID – Five years on, the addition of the CDK4/6 inhibitor abemaciclib (Verzenio) to endocrine therapy for women with high-risk hormone receptor–positive, HER2-negative (HR+/HER2–) early breast cancer continues to show modest but clinically significant benefits, compared with endocrine therapy alone.
Results of a planned 5-year efficacy analysis of the monarchE trial showed that , reported Nadia Harbeck, MD, from the Breast Center at Ludwig Maximilians University Hospital in Munich.
“The data are consistent with a carryover effect and further support the addition of adjuvant abemaciclib to endocrine therapy for patients with hormone receptor–positive, HER2-negative, node-positive high-risk early breast cancer,” she said at the 2023 European Society for Medical Oncology Congress.
High recurrence risk
Although HR+/HER2– breast cancer, the most common subtype of breast cancer, is generally associated with better outcomes than other subtypes, patients with node-positive early disease are at high risk for early recurrence and need treatment intensification, Dr. Harbeck said.
The monarchE trial included two cohorts: a primary cohort consisting of patients deemed at high risk based on clinical pathological features such as the number of involved axillary nodes, grade 3 disease, and tumors 5 cm or larger, and a second cohort of patients with lower disease grade and smaller tumors but with high levels of the proliferation marker Ki-67.
A total of 5,637 patients were randomized to receive either 2 years of abemaciclib 150 mg twice daily plus endocrine therapy, or endocrine therapy alone, followed by 3-8 years of additional endocrine as clinically indicated in each study arm.
An earlier preplanned interim analysis of the phase 3 trial of more than 5,600 patients was presented at the ESMO Virtual Congress 2020, and simultaneously published in the Journal of Clinical Oncology.
As that analysis showed, at a median follow-up of 15.5 months abemaciclib plus endocrine therapy was associated with a 25% relative risk reduction in the primary endpoint of IDFS vs. endocrine therapy alone.
At the time, the findings were hailed as practice-changing and, once approved for high-risk HR+/HER2-negative early breast cancer, as the new standard of care.
In the current analysis, Dr. Harbeck and colleagues looked at 5-year outcomes from a prespecified analysis, with a data cutoff of July 3, 2023.
All patients originally assigned to abemaciclib are now off the drug, and more than 80% have been followed for a minimum of 2 year since completing therapy with the CDK4/6 inhibitor.
Results
At 5 years there were cumulative totals of 407 IDFS events in the combination arm, compared with 585 in the endocrine therapy alone arm, a difference that translated into a hazard ratio of 0.68 favoring abemaciclib (P < .001).
The IDFS benefit with the combination was consistent across most subgroups, including older patients, perimenopausal and postmenopausal patients, those who had received prior neoadjuvant or adjuvant chemotherapy, all tumor sizes, number of positive lymph nodes, less favorable tumor stage or grade, and order of endocrine therapy (tamoxifen or aromatase inhibitor as first drug).
As noted before, DRFS, a secondary endpoint, also favored abemaciclib, with 345 events occurring over 5 years in the combination arm, compared with 501 in the endocrine therapy arm alone. This translated into a HR with the combination of 0.68 (P < .001).
There were fewer deaths in the abemaciclib arm (208 vs. 234), but this difference was not statistically significant.
The proportions of patients with treatment-emergent adverse events and serious adverse events (SAEs) were higher in the combination arm than in the endocrine therapy alone arm in all previous analyses of the trial data.
In the current analysis, “I would say it’s reassuring to see that the SAEs reported in the follow-up period, after the study treatment had been completed, are quite similar between the endocrine therapy alone arm and the abemaciclib plus endocrine therapy arm,” Dr. Harbeck said.
