Background
Phase 3, open-label, randomized. HER2+ (ERBB2+) advanced breast cancer after ≥2 prior anti-HER2 therapies and 1-3 lines for metastatic disease. Margetuximab is an Fc-engineered anti-HER2 antibody (trastuzumab epitope) with enhanced CD16A binding to boost antibody-dependent cytotoxicity. N=536 (margetuximab 266 vs trastuzumab 270); ~91% prior T-DM1, nearly all prior pertuzumab.
Results
Interventions and follow up: Arm A: margetuximab 15 mg/kg IV q3wk + investigator's choice chemotherapy (n=266).
Arm B: trastuzumab 6 mg/kg IV q3wk (8 mg/kg load) + same chemotherapy (n=270).
Primary endpoint: sequential — PFS by central blinded review, then OS.
Results: PFS (central): 5.8 vs 4.9 mo, HR 0.76, 95% CI 0.59–0.98, P=.03 (24% relative risk reduction).
ORR: 22% vs 16%.
OS (2nd interim): 21.6 vs 19.8 mo, HR 0.89, 95% CI 0.69–1.13, P=.33.
OS (final, JCO 2022): 21.6 vs 21.9 mo, HR 0.95, 95% CI 0.77–1.17, P=.62 (NOT significant).
Exploratory: benefit concentrated in CD16A-158F carriers (hypothesis-generating).
Arm B: trastuzumab 6 mg/kg IV q3wk (8 mg/kg load) + same chemotherapy (n=270).
Primary endpoint: sequential — PFS by central blinded review, then OS.
Results: PFS (central): 5.8 vs 4.9 mo, HR 0.76, 95% CI 0.59–0.98, P=.03 (24% relative risk reduction).
ORR: 22% vs 16%.
OS (2nd interim): 21.6 vs 19.8 mo, HR 0.89, 95% CI 0.69–1.13, P=.33.
OS (final, JCO 2022): 21.6 vs 21.9 mo, HR 0.95, 95% CI 0.77–1.17, P=.62 (NOT significant).
Exploratory: benefit concentrated in CD16A-158F carriers (hypothesis-generating).
Adverse events
Infusion-related reactions: 13.3% (margetuximab) vs 3.4% (trastuzumab), mostly cycle 1.
Overall: safety comparable between arms, including cardiac events.
Overall: safety comparable between arms, including cardiac events.
Conclusions
In heavily pretreated HER2+ advanced breast cancer, margetuximab + chemotherapy gave a statistically significant but small PFS gain over trastuzumab + chemotherapy, with comparable safety apart from more infusion reactions. The final OS analysis was negative, and the CD16A genotype findings were hypothesis-generating only.
Key Limitations
Absolute PFS gain <1 month, of uncertain clinical significance. Final OS showed no survival advantage (HR 0.95, P=.62). The CD16A subgroup signal rested on small, non-prespecified exploratory comparisons, was directionally inconsistent (favoring trastuzumab in CD16A-158VV patients), and has not been prospectively validated. Open-label design.
Clinical Context
Led to FDA accelerated approval (Dec 2020, MARGENZA) for pretreated HER2+ metastatic breast cancer, on PFS. The modest PFS benefit, absent OS gain, and unconfirmed CD16A hypothesis have left it a niche option; ESMO/ASCO sequencing now prioritizes more active later-line agents such as trastuzumab deruxtecan and tucatinib-based regimens, which carry stronger efficacy data in this setting.