CHICAGO – Adding ribociclib to endocrine therapy significantly improved overall survival of premenopausal women with advanced hormone receptor positive, HER2-negative breast cancer, results of the randomized phase 3 MONALEESA-7 trial showed.
A landmark analysis conducted at 42 months showed that the overall survival rate for women randomized to receive endocrine therapy with either a nonsteroidal aromatase inhibitor (AI) or tamoxifen plus the cyclin-dependent kinase 4/6 (CDK4/6) inhibitor ribociclib was 70%, compared with 46% for women randomized to endocrine therapy alone, reported Sara A Hurvitz, MD, of the University of California Los Angeles Jonsson Comprehensive Cancer Center
“This is the first time a statistically significant improvement in overall survival has been observed with a CDK4/6 inhibitor in combination with endocrine therapy in patients with hormone receptor-positive advanced disease,” she said at a briefing prior to her presentation of the data in an oral abstract session at the American Society of Clinical Oncology annual meeting.
“This is an important study, because it shows that the class of drugs, CDK4/6 inhibitors, which we are widely using, has been shown to delay the time to progression, delay the time to need for chemotherapy for advanced breast cancer, and really doubled the effectiveness of endocrine therapy, now also translates into a significant survival benefit for women who ER-positive metastatic breast cancer,” commented Harold J. Burstein, MD, PhD, an ASCO expert from the Dana-Farber Cancer Institute in Boston.
In the trial, 672 pre- or perimenopausal women with HR+/HER2– advanced breast cancer with no prior endocrine therapy for advanced disease and no more than one line of chemotherapy for advanced disease were enrolled. The patients were stratified by the presence of liver/lung metastases, prior chemotherapy, and prior endocrine partner, tamoxifen or nonsteroidal AI, and then randomly assigned to ribociclib 600 mg/day for 3 weeks, followed by 1-week off, plus tamoxifen or AI and goserelin, or the same combination and schedule with placebo.
Of the 672 patients enrolled, a total of 335 patients assigned to ribociclib and 337 assigned to placebo received treatment. The majority of patients – 495 – received an AI, either letrozole (Femara) or anastrozole (Arimidex). Dr. Hurvitz noted that after the initiation of MONALEESA-7, the combination of a CDK4/6 inhibitor and tamoxifen was found to prolong the QT interval and increase risk for cardiac arrhythmias, and is now contraindicated.
As, results of the primary MONALEESA-7 endpoint of progression-free survival favored the combination, with a median PFS of 23.8 months, compared with 13 months for women treated with endocrine therapy alone. The hazard ratio for progression with the ribociclib-based combination was 0.553 ( P less than .0001), and the treatment benefit of the CDK4/6 inhibitor was seen across all patients subgroups and regardless of the endocrine partner.
At ASCO 2019, Dr. Hurvitz reported on the key secondary endpoint of overall survival. At a median follow-up duration of 34.6 months, with an additional 15 months beyond the initial analysis, the median OS for the ribociclib arm was not reached, compared with 40.9 months in the placebo arm. The hazard ratio for death with ribociclib was 0.712 ( P = .00973). An analysis of OS by endocrine partner subgroup showed no significant differences between AIs or tamoxifen.
At the time of the data cutoff, 35% of patients in the ribociclib arm were still on therapy.
The safety and tolerability of the combination were consistent with those previously reported, Dr. Hurvitz said.
“In an era when we are thinking about value in oncology care, a demonstration of a robust sutvival difference I think substantially adds to a value proposition for products like ribociclib that were discussed here,” Dr. Burstein said.
“Hopefully, these data will enable access to this product to more women around the world, particularly in health care systems that assess value rigorously as part of their decisions for national access to drugs,” he added.
The MONALEESA-7 trial is supported by Novartis. Dr. Hurvitz reported travel and accommodation expenses from Novartis. Dr. Burstein reported no relevant disclosures.
SOURCE: Hurvitz SA et al. ASCO 2019. .