Updated Overall Survival Data in Patients Treated with Ribociclib plus Fulvestrant

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The combination of ribociclib plus fulvestrant has demonstrated significant progression-free survival and overall survival (OS) benefits in patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer (ABC). In a new landmark study, Slamon and colleagues presented follow-up survival data for a phase 3 cyclin-dependent kinases 4 and 6 inhibitor clinical trial in patients with ABC.

This large phase 3, double-blind, randomized, placebo-controlled trial was conducted at 174 sites in 30 countries. It included both male and postmenopausal female patients who were ≥18 years of age with either cytologically or histologically confirmed HR-positive, HER2-negative ABC. Patients included in the trial could have received ≥1 line of endocrine therapy (ET) but no chemotherapy for ABC. Patients were assigned to treatment in a 2:1 ratio and were stratified by the absence or presence of liver/lung metastases and previous ET. Patients received placebo or intramuscular fulvestrant at a dose of 500 mg, on day 1 of each 28-day cycle plus day 15 of cycle 1, with oral ribociclib (600 mg/day, 3 weeks on, 1 week off). In patients treated with ≥1 dose of the study regimen, safety was assessed. Overall survival was a secondary end point.

In the 1-year period between June 2015 and June 2016, a total of 726 patients were randomly assigned to receive ribociclib (n = 484) or placebo (n = 242). Data cut-off was in October 2020, with a median OS (mOS) of 53.7 months in the ribociclib-treated arm, compared with 41.5 months in the placebo-treated arm. Notable subgroups included the absence or presence of liver or lung metastases and response to prior ET. In the first-line setting, results were remarkable; the majority of patients receiving ribociclib treatment (approximately 60%) lived longer than median follow-up, where the mOS was 51.8 months. The mOS was 39.7 months in the ribociclib-treated arm compared with 33.7 months in the placebo arm, in the second-line setting. In addition, no new safety signals or apparent drug–drug interactions were observed.

The researchers concluded that, based on their analysis, in which there was an extended OS follow-up in MONALEESA-3, the mOS was approximately 1 year longer in patients with HR-positive, HER2-negative ABC treated with ribociclib plus fulvestrant compared with fulvestrant monotherapy.

Source

Slamon DJ, Neven P, Chia S, et al. Ribociclib plus fulvestrant for postmenopausal women with hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer in the phase III randomized MONALEESA-3 trial: updated overall survival [published correction appears in Ann Oncol. 2021;32:1307]. Ann Oncol. 2021;32:1015-1024.

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