MacroGenics’ trial compared its margetuximab candidate + chemotherapy to Herceptin + chemotherapy in HER2+ metastatic breast cancer patients who have previously received at least 2 prior anti-HER2 therapies, including Perjeta and 1-3 lines of prior treatment.
Margetuximab is a monoclonal antibody targeted to HER2. Macrogenics is positioning margetuximab as a ‘better Herceptin’ with an improved ADCC and engineered to target specific genotypes that might be resistant to Herceptin and because of this the choice to compare to Herceptin makes sense.
Data was presented for the intent-to-treat population in which margetuximab was able to significantly improve median PFS by a modest 1 month benefit. But the level of benefit was doubled in patients with CD16A genotypes with a 158F allele.
In patients with baseline measurable disease, margetuximab produced an overall response rate of 22% compared to 16% in Herceptin arm. Immature OS analysis was shown, but there was not a significant difference.
The two arms produced mostly similar safety profiles, although margetuximab was associated with increased rates of infusion related reactions.
While the combination of margetuximab + chemotherapy did significantly improve PFS, the fact that it was only one month leaves us asking if this will be clinically relevant in all patients or only in the select population with CD16A genotypes.