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Longest survival benefit from first-line CDK4/6 inhibitor

Presented By
Prof. Gabriel Hortobagyi, University of Texas MD Anderson Cancer Center, USA
ESMO 2021
Phase 3, MONALEESA-2
CDK4/6 inhibitor ribociclib added to endocrine therapy extended overall survival (OS) in treatment-naïve postmenopausal patients with HR-positive, HER2-negative, advanced, metastatic breast cancer. Data from the MONALEESA-2 trial showed that after a median follow-up of >6.5 years, median OS was 12 months longer for first-line ribociclib plus letrozole versus placebo plus letrozole.

Prof. Gabriel Hortobagyi (University of Texas MD Anderson Cancer Center, USA) presented the late-breaking results highlighting the final OS analysis of the phase 3 MONALEESA-2 study (NCT01958021), which evaluated ribociclib (oral, 600 mg daily, 3 weeks on/1 week off) plus the aromatase inhibitor letrozole (oral, 2.5 mg daily), compared with placebo plus letrozole [1]. The primary endpoint of MONALEESA-2 (n=668) was met and reported previously, showing that ribociclib plus letrozole improved progression-free survival of postmenopausal women with HR-positive, HER2-negative, metastatic breast cancer [2]. Furthermore, the results of the MONALEESA-7 trial in premenopausal patients with advanced HR-positive, HER2-negative breast cancer reported an improved progression-free survival and OS benefit [3,4]. OS was a key secondary endpoint of MONALEESA-2, and long-term OS data were presented at ESMO 2021 .

With a median follow-up of 79.7 months, the final analysis of MONALEESA-2 showed a median OS of 63.9 months with frontline ribociclib and letrozole, compared with 51.4 months with letrozole alone. The estimated 6-year survival rate was 44.2% with ribociclib versus 32% for placebo. MONALEESA-2 is the first trial to demonstrate a survival advantage with a frontline CDK4/6 inhibitor in combination with an aromatase inhibitor in postmenopausal patients with HR-positive, HER2-negative, advanced breast cancer.

No new safety signals were observed with this longer follow-up, and adverse events were consistent with earlier reported MONALEESA trial results.

Prof. Hortobagyi concluded, “I am very encouraged that metastatic breast cancer patients may have a treatment option that extends survival, delays chemotherapy treatment and preserves their quality of life.” To date, this is the first report of a statistically significant and clinically meaningful OS benefit with a first-line CDK4/6 inhibitor in postmenopausal patients with HR-positive, HER2-negative, advanced breast cancer.

  1. Hortobagyi GN, et al. Overall survival (OS) results from the phase III MONALEESA-2 (ML-2) trial of postmenopausal patients (pts) with hormone receptor positive/human epidermal growth factor receptor 2 negative (HR+/HER2−) advanced breast cancer (ABC) treated with endocrine therapy (ET) ± ribociclib (RIB). Abstract LBA17_PR, ESMO Congress 2021, 16–21 September.

  2. Hortobagyi GN, et al. Ann Oncol. 2019;30(11):1842.

  3. Tripathy D, et al. Lancet Oncol. 2018;19(7):904-915.

  4. Im SA, et al. N Engl J Med. 2019 Jul 25;381(4):307-316.


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