Summary

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• Margenza (margetuximab-cmkb) is indicated in combination with chemotherapy for the treatment of adult patients with metastatic HER2-positive breast cancer who have received two or more prior anti-HER2 regimens, at least one of which was for metastatic disease.
• This summary is based on the review of three randomized controlled trials. ^[1-3]
• Progression-Free Survival (PFS): Margetuximab significantly improved PFS over trastuzumab, with a 24% relative risk reduction (HR, 0.76; 95% CI, 0.59-0.98; P = .03), extending median PFS to 5.8 months compared to 4.9 months for trastuzumab.
• Overall Survival (OS): There was no statistically significant difference in OS between margetuximab and trastuzumab, with median OS of 21.6 months for margetuximab versus 21.9 months for trastuzumab (HR, 0.95; 95% CI, 0.77 to 1.17; P = .620).
• Objective Response Rate (ORR): Margetuximab showed an improved ORR compared to trastuzumab, increasing from 16% to 22% in one analysis (P = .06) and from 14% to 25% in another analysis (P < .001).
• Safety Profile: Margetuximab had a safety profile comparable to trastuzumab, with the exception of a higher incidence of infusion-related reactions in the margetuximab group (13.3% vs. 3.4%).
• Adverse Events Across Subgroups: The safety of margetuximab was manageable across all chemotherapy subgroups, with fewer high-grade adverse events noted among subjects receiving capecitabine.
• Subgroup Findings: Margetuximab showed a possible improvement in OS for CD16A-158FF patients (median OS, 23.6 vs. 19.2 months; HR, 0.72; 95% CI, 0.52 to 1.00) and a potential disadvantage for CD16A-158VV patients (median OS, 31.1 vs. 22.0 months; HR, 1.77; 95% CI, 1.01 to 3.12). Additionally, in chemotherapy subgroups, margetuximab had variable toxicity and fewer high-grade adverse events in subjects receiving capecitabine, with the lowest PFS hazard ratios favoring margetuximab in those receiving eribulin or gemcitabine, though statistical significance was not achieved.