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Study Shows Tolerable Safety of Abemaciclib Plus Pembrolizumab in HER2-, Metastatic Breast Cancer

Researchers explored abemaciclib with pembrolizumab in a multicenter, nonrandomized, open-label phase Ib among endocrine resistant hormone receptor positive (HR+), HER2- metastatic breast cancer patients on continuous, twice-daily dosing as monotherapy or in combination with an aromatase inhibitor, or in combination with fulvestrant.

In previous murine models, abemaciclib as monotherapy has increased tumor immunogenicity and aligned with anti-PD-1 to improve antitumor efficacy, according to Hope S. Rugo, MD, professor and director, Breast Oncology and Clinical Trials Education, UCSF, and fellow researchers, in a study abstract from the American Society of Clinical Oncology Annual Meeting.
 
Patients received 150 mg oral abemaciclib every 12 hours plus intravenous pembrolizumab 200 mg on day 1 and every 21 days. Prior CDK4/6 inhibitor use was prohibited.  
 
While the primary objective was to quantify the safety of the drug combination, the secondary objectives included objective response rate, progression-free survival and overall survival.
 
Safety was generally manageable and consistent with the known side effects of abemaciclib and pembrolizumab, according to researchers. 

A partial response was confirmed in eight patients (29% ORR) and disease control rate was 82%. The clinical benefit rate was 46% (CR+PR+SD persisting for ≥6 months).

Median PFS was 8.9 months (95% CI 3.9, 11.1) and OS was 26.3 months (95% CI 20.0, 31.0).

The combination of abemaciclib plus pembrolizumab “demonstrated a generally tolerable safety profile with numerically higher rate of transaminase elevations than reported for the individual treatments,” according to the researchers.

When compared to historical data for abemaciclib monotherapy in a similar patient population, the researchers noted a numerically higher but “not obviously different” ORR, PFS and OS.


By MD /alert Staff

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