Ribociclib regimen extends OS in advanced breast cancer
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The addition of ribociclib to front-line letrozole prolonged OS among postmenopausal women with hormone receptor-positive, HER2-negative advanced breast cancer, results of the randomized phase 3 MONALEESA-2 trial showed.
The findings — presented during the virtual ESMO Congress 2021 — are the first to show a statistically significant OS benefit in this patient population, according to the investigators.
“Previous studies have shown that [cyclin-dependent kinase] 4/6 inhibitors in combination with standard hormonal treatment prolong the duration of disease control [or] PFS by approximately 1 year,” Gabriel N. Hortobagyi, MD, FACP, professor of medicine in the breast medical oncology division of The University of Texas MD Anderson Cancer Center, said in an ESMO-issued press release. “These drugs were subsequently approved by the regulatory agencies and have been available for patients with [hormone receptor]-positive, HER2-negative advanced breast cancer. [The current] results add to this by showing that the CDK 4/6 inhibitor ribociclib [Kisqali, Novartis] extends survival by 1 year.”
The MONALEESA-2 trial included 668 postmenopausal women previously untreated for their advanced disease. Researchers randomly assigned 334 patients to 2.5 mg daily letrozole plus placebo. The other 334 patients received letrozole plus 600 mg daily ribociclib.
PFS served as the study’s primary endpoint. Secondary endpoints included OS, overall response rate, clinical benefit rate and safety.
Previously reported results showed a statistically significant PFS improvement among ribociclib-treated patients (25.3 months vs. 16 months).
At ESMO, Hortobagyi presented final OS data, analyzed after 400 deaths had occurred. Median follow-up was 79.7 months.
Results showed a statistically significant OS improvement among patients assigned ribociclib vs. placebo (63.9 months vs. 51.4 months; HR = 0.76; 95% CI, 0.63-0.93).
Researchers also reported a higher estimated 6-year OS rate (44.2% vs. 32%), longer median chemotherapy-free survival (39.9 months vs. 30.1 months; HR = 0.74; 95% CI, 0.62-0.89) and longer median time to first chemotherapy (50.6 months vs. 38.9 months; HR = 0.74; 95% CI, 0.61-0.91) with ribociclib.
Investigators observed no new safety signals.
“To put these results into perspective, in my 45 years as an oncologist there have been tens of thousands of clinical trials for breast cancer and — [although] a PFS benefit has been shown many, many times — we have rarely observed an improvement in [OS],” Hortobagyi said in the release. “It is difficult to show a statistically significant extension in survival for first-line therapy in this type of breast cancer because, due to the development of resistance, patients receive four to 15 different types of treatment during the course of their disease, and these dilute the effect of the first therapy.”
Researchers are awaiting results of trials investigating palbociclib (Ibrance, Pfizer), abemaciclib (Verzenio, Eli Lilly) and other treatments — including additional kinase inhibitors — as treatment options for this patient population.
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Hortobagyi GN, et al. Abstract LBA17. Presented at: European Society for Medical Oncology Congress (virtual meeting); Sept. 17-21, 2021.
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