- Although the phase 2 nextMONARCH trial of women with heavily pretreated HR+/HER2- metastatic breast cancer was not powered to test superiority with regard to overall survival (OS), there was a statistically significant improvement of 7.2 months (24.2 vs. 17.0) with the addition of tamoxifen to abemaciclib compared to abemaciclib monotherapy.
Why this matters?
- Abemaciclib is an oral, continuously dosed cyclin-dependendent kinase 4 & 6 inhibitor approved in the US and EU for patients with HR+/HER2- metastatic breast cancer (MBC) following progression from endocrine therapy (ET) alone.
- A series of studies and have reported improved progression free survival (PFS) for abemaciclib in combination with endocrine therapy (MONARCH2, MONARCH3) or robust single-agent activity (nextMONARCH), but no OS data yet.
- nextMONARCH was a multicenter randomized, open-label phase 2 trial of abemaciclib that enrolled 234 women with heavily pretreated HR+, HER2- MBC whose disease progressed on or after ET and chemotherapy.
- Patients were randomized 1:1:1 to abemaciclib 150 mg + tamoxifen 20 mg (A), or abemaciclib 150 mg (B) or abemaciclib 200 mg plus prophylactic loperamide (C).
- Funding: Eli Lilly and Company
- Updated PFS at 183 events: A – 9.07 months, B – 7.20 months, C – 7.43 months. Hazard ratio (HR) A/C, 0.81 (not significant, P=.249)
- Median OS A – 24.2 months, B – 20.8 months, C – 17.0 months. HR A/C, 0.62 (P=.034)
- By adding loperamide, the incidence of grade 3 diarhea was reduced to 9% as compared to 20% in MONARCH1.
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