Final overall survival (OS) for abemaciclib plus trastuzumab +/- fulvestrant versus t
Final overall survival (OS) for abemaciclib plus trastuzumab +/- fulvestrant versus trastuzumab plus chemotherapy in patients with HR+, HER2+ advanced breast cancer (monarcHER): A randomized, open-label, phase II trial
Abstract LBA18
Background
Abemaciclib, an oral, selective CDK4 & 6 inhibitor, significantly improved PFS in HR+, HER2+ advanced breast cancer (ABC; locoregionally recurrent or metastatic) when combined with fulvestrant and trastuzumab, compared to trastuzumab plus chemotherapy in monarcHER (Tolaney 2020, Lancet Oncol.) Here, we report the OS results at the prespecified final analysis.
Methods
monarcHER (NCT02675231) is a randomized, multicenter, open-label phase 2 trial. Randomization was 1:1:1 to arm A (abemaciclib 150mg PO BID, trastuzumab IV, fulvestrant 500mg IM), arm B (abemaciclib, trastuzumab), and arm C (trastuzumab, SOC chemotherapy). Stratification factors were number of prior systemic regimens for ABC and measurable disease. Exploratory biomarker analyses were also conducted, including evaluation of intrinsic subtypes by RNAseq.
Results
At the time of data cutoff (31 Mar 2022), of the 237 patients enrolled, 157 deaths had occurred across the treatment arms, 50 deaths (63%) arm A, 54 deaths (68%) arm B, and 53 deaths (67%) arm C. Median follow-up was 52.9 months. mOS was 30.3 months in arm A, 31.43 months in arm B and 22.7 months in arm C (A v C: HR 0.75 [95% CI 0.47, 1.21]; nominal 2-sided p-value 0.243; B v C: HR 0.73 [95% CI 0.46, 1.15]; nominal 2-sided p-value 0.177). In exploratory RNAseq analyses, luminal subtypes were associated with longer PFS (8.6 v 5.4 months [HR 0.54, 95% CI 0.38, 0.79]) and OS (31.7 v. 19.7 months [HR 0.68, 95% CI 0.46, 1]) compared to non-luminal. Updated PFS and safety findings were consistent with the primary analysis (data cutoff 8 Apr 2019).
Conclusions
Abemaciclib plus trastuzumab ± fulvestrant numerically improved OS in women with HR+, HER2+ ABC compared to chemotherapy plus trastuzumab with a manageable safety profile.
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