BARCELONA – In postmenopausal women with hormone receptor–positive, HER2-negative advanced breast cancer, the combination of ribociclib (Kisqali) and fulvestrant (Faslodex) was associated with a significant survival benefit, compared with fulvestrant alone, investigators reported.
Neil Osterweil/MDedge News
Dr. Dennis J. Slamon
Among 726 postmenopausal patients in MONALEESA-3 randomly assigned to receive either ribociclib or placebo plus fulvestrant who were followed for a median of 39.4 months, the median overall survival (OS) was not reached for patients assigned to ribociclib, compared with 40 months for patients in the control (fulvestrant-only) arm, reported Dennis J. Slamon, MD, PhD from the University of California, Los Angeles
“The combined data set of MONALEESA-3 and MONALEESA-7 represent some 1,400 patients, and the largest body of evidence for overall survival for any [cyclin-dependent kinases 4/6] inhibitor, and these data demonstrate a consistent, meaningful prolongation of survival irrespective of menopausal status, pre or post, and irrespective of whether the patient is treated in the first line or the second line,” he said at the European Society for Medical Oncology Congress.
Results of the MONALEESA-7 trial, which showed an overall survival advantage for adding ribociclib to endocrine therapy in premenopausal women with hormone receptor–positive, HER2-negative breast cancer, were reported at the 2019 annual meeting of the American Society of Clinical Oncology.
MONALEESA-3 investigators enrolled 726 postmenopausal women with hormone receptor–positive/HER2-negative advanced breast cancer who had received not more than one prior line of endocrine therapy for advanced disease, stratified them by the presence of liver and/or lung metastases and prior endocrine therapy, and then randomly assigned them to receive intramuscular fulvestrant 500 mg every 28 days, with an additional dose on day 15 of cycle one, plus either ribociclib 600 mg per day, 3 weeks on and 1 week off for every cycle, or placebo.
Dr. Slamon presented results of the primary endpoint of progression-free survival at the 2018 ASCO annual meeting, which showed a median PFS with ribociclib plus fulvestrant of 20.5 months versus 12.8 months for fulvestrant alone (hazard ratio, 5.93; P less than .0001). The overall survival data presented by Dr. Slamon at ESMO 2019 were not mature at that time.
As noted, at a median follow-up of 39.4 months, median overall survival was not reached in the combination arm, compared with 40 months in the fulvestrant/placebo arm, translating into a HR for risk of death with ribociclib of 0.724 (P = .00455).
Estimated OS rates at 36 months were 67% in the ribociclib arm versus 58.2% in the placebo arm, and at 42 months were 57.8% and 45.9%, respectively.
The survival benefit appeared consistent both for patients treated in the first line (median OS not reached vs. 45.1 months; HR, 0.70) and for those treated after early relapse of therapy for early breast or in the second line (median OS, 40.2 vs. 32.5 months, respectively; HR, 0.73). In both comparisons, however, the 95% confidence interval crossed 1, indicating that the results were not statistically significant.
An analysis of OS by subgroup indicated significant benefit or trends for most categories except Asian race, and treatment in Asia or Latin America, although the numbers of patients in each of those subgroups was less than 20, making it difficult to draw significant inferences from the findings, Dr. Slamon cautioned.
A descriptive analysis of updated PFS results were very similar to those previously reported, with a median of 20.6 months with ribociclib versus 12.8 months with placebo (HR, 0.587). Median PFS by line of therapy was 33.6 versus 19.2 months, respectively, in the first line, and 14.5 versus 9.1 months in the second line (HR, 0.546 and 0.571; P values not shown).
Neil Osterweil/MDedge News
Dr. Sybil Loibl
“CDK4/6 inhibitors not only improve progression-free survival in first- and second-line metastatic breast cancer, it also translates into an overall survival improvement. What more do we really want?” said invited discussant Sybil Loibl, MD, from Goethe University in Frankfurt, Germany.
“Outcome improves irrespective of pretreatment, menopausal status, endocrine sensitivity and site of metastases, which is good knowledge for our patients,” she said.
To date there are no biomarkers identified that can select subgroups that could experience particular benefit from CDK4/6 inhibitors. It may require a meta-analysis of all available clinical trial data on these agents in both the first and second line therapy to reveal potential differences among subgroups, she said.
MONALEESA-3 is supported by Novartis. Dr. Slamon disclosed a consulting or advisory role, research funding, honoraria, and travel expenses from Novartis and others. Dr. Loibl disclosed honoraria and research grants from Novartis and others.
SOURCE: Slamon DJ et al. ESMO 2019, Abstract LBA7_PR.