MONARCH 2: Abemaciclib plus fulvestrant
In the MONARCH 2, randomized, placebo-controlled, phase 3 trial, abemaciclib plus fulvestrant (abema-F) significantly improved PFS, in comparison with placebo plus fulvestrant (placebo-F; 16.9 months vs. 9.3 months; HR, 0.563) in 669 premenopausal (with concurrent ovarian function suppression) and postmenopausal women with metastatic breast cancer (mBC) who had disease progression on one to two lines of prior hormonal therapy (J Clin Oncol. 2017;35[25]:2875-84).
At ESMO 2019, George W. Sledge Jr., MD, of Stanford (Calif.) Medical Center, and colleagues reported the OS results, a secondary endpoint for the trial (JAMA Oncol. 2019 Sep 29. doi. 10.1001/jamaoncol.2019.4782). At the prespecified interim analysis point, median OS for abema-F was 46.7 months vs. 37.3 months for placebo-F (HR, 0.757; 95% CI 0.505-0.945; P = .0137). Patients with greatest benefit from abema-F were exactly the patients who needed the most help – those with visceral metastases (HR 0.675) and with primary resistance to prior hormonal therapy (HR, 0.686).
At 3 years, at least three times as many patients remained progression free with abema-F, compared with placebo-F, and the abema-F patients experienced prolongation in time to eventual chemotherapy (50.2 months vs. 22.1 months; HR, 0.625).
What this means in clinical practice
Many times I find myself sitting at the annual meeting of the American Society of Clinical Oncology and thinking, “Only a medical oncologist like me would find this result exciting.” Prior to ESMO 2019, MONARCH 2 (and a similar study presented at ESMO 2019, MONALEESA-3, which employed an alternative CDK 4/6 inhibitor, ribociclib, with similar OS results) added to the body of literature that caused NCCN guidelines to list all of the approved CDK 4/6 inhibitors plus endocrine therapy for first- or second-line use in patients with hormone-receptor positive, HER2/neu-negative mBC. NCCN guidelines have the caveat that, among patients with disease progression on CDK 4/6 inhibitors in the first-line setting, there are no data to support continuing the CDK 4/6 inhibitor or switching to an alternative CDK 4/6 inhibitor thereafter.
For that shrinking group of patients and doctors who choose to avoid CDK 4/6 inhibitors for first-line treatment, as we describe risks and benefits of using a CDK 4/6 inhibitor for second- or third-line therapy, we have high-quality OS information from ESMO 2019 to answer the “Is it worth it?” question.
Are the results of MONARCH 2 and MONALEESA-3 practice changing? No. We were already convinced. Should we be excited that we have this new information for discussions with our patients? Absolutely.
Dr. Lyss has been a community-based medical oncologist and clinical researcher for more than 35 years, practicing in St. Louis. His clinical and research interests are in the prevention, diagnosis, and treatment of breast and lung cancers and in expanding access to clinical trials to medically underserved populations.