Premenopausal women with hormone receptor–positive or negative advanced breast cancer who received ribociclib in combination with endocrine therapy lived nearly a year longer without disease progression than woman who received endocrine therapy alone, according to recent research presented at the ASCO 2019 Annual Meeting.
“This is the first study to show improved survival for any targeted therapy when used with endocrine therapy as a first-line treatment for advanced breast cancer,” Sara A. Hurvitz, MD, director of the Breast Cancer Clinical Research Program at UCLA Jonsson Comprehensive Cancer Center in Los Angeles, Calif., stated in a press release. “The use of ribociclib as a front-line therapy significantly prolonged overall survival, which is good news for women with this terrible disease.”
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In the phase 3 MONALEESA-7 study, 672 patients with HER-positive or negative advanced breast cancer were randomized to receive the tablet form of cyclin-dependent kinase 4/6 (CDK4/6) inhibitor ribociclib plus endocrine therapy, or a placebo tablet plus endocrine therapy. Endocrine therapy consisted of goserelin and either tamoxifen, or nonsteroidal aromatase inhibitor letrozole or anastrozole. At median follow-up of 34.6 months, 173 patients continued to receive treatment, with 116 patients in the ribociclib group and 57 patients in the placebo group. Use of post-treatment therapy occurred for 68.9% of patients receiving ribociclib plus endocrine therapy and 73.2% of patients receiving placebo.
Progression-free survival for patients in the ribociclib group was 23.8 months compared with 13.0 months in the placebo group (hazard ratio, 0.55; 95% confidence interval, 0.44-0.69; P < .0001). Overall survival (OS) was also significantly improved for patients receiving ribociclib (median not yet reached) compared with patients receiving placebo (median 40.9 months) and endocrine therapy (HR, 0.712; 95% CI, 0.54-0.95; P =.00973). “The result crossed the prespecified stopping boundary for superior efficacy,” the researchers said.
At 42 months, there was an estimated OS of 70.2% for ribociclib patients compared with 46.0% in the placebo group for a relative risk reduction of 29% among patients receiving ribociclib plus endocrine therapy.
There was also an improvement in OS for patients who received ribociclib plus a nonsteroidal aromatase inhibitor (495 patients) such as letrozole or anastrozole (HR, 0.699; 95% CI, 0.50-0.98).
Dr. Hurvitz and colleagues said they are currently examining patient-reported outcomes and clinical findings to determine which patients are likely to see a benefit from receiving ribociclib in combination with endocrine therapy as well as for men and women with HER2-positive and negative breast cancer and other cancers.