Adding ribociclib to letrozole is well tolerated, and significantly improves progression-free survival compared with letrozole alone, among postmenopausal, treatment-naive patients with hormone receptor-positive (HR+), HER2-negative (HER2–) advanced breast cancer, according to a study presented at the European Society for Medical Oncology (ESMO) 2016 Congress.1

Although endocrine therapy is frequently used as first-line therapy for advanced breast cancer, most patients eventually develop resistance and disease progression occurs. Ribociclib is a cyclin-dependent kinase 4/6 inhibitor that may help to overcome or delay resistance to endocrine therapy. Researchers evaluated the efficacy and safety of ribociclib plus letrozole as first-line therapy for patients with HR+, HER2– advanced breast cancer.

For the multicenter, double-blind, phase 3 MONALEESA-2 study ( Identifier: NCT01958021), investigators enrolled 668 patients who had received no prior therapy for advanced disease. Participants were randomly assigned 1:1 to receive letrozole plus ribociclib or placebo.

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An interim analysis showed that median progression-free survival had not yet been reached (95% CI, 19.3-not estimable) in the ribociclib arm, versus 14.7 months (95% CI, 13.0-16.5) in the placebo arm. Patients treated with ribociclib had a 44% reduced risk of progression or death compared with those who received letrozole alone (hazard ratio, 0.556; 95% CI, 0.429-0.720; P = .00000329).

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Fifty-three percent of ribociclib-treated patients achieved a response versus 37% of those in the placebo group (P = .00028). The clinical benefit rate was 80% and 72%, respectively (P = .02).

The rates of discontinuation due to adverse events were 7.5% in the ribociclib arm and 2.1% in the placebo arm, respectively.                           


  1. Hortobagyi GN, Stemmer SM, Burris HA, et al. First-line ribociclib + letrozole for postmenopausal women with hormone receptor-positive (HR+), HER2-negative (HER2–), advanced breast cancer (ABC). Paper presented at: European Society for Medical Oncology (ESMO) 2016 Congress; October 7-11, 2016; Copenhagen, Denmark.