ESMO Quick Takes: MacroGenics’ early proof of concept for B7-H3 ADC

Investors were disappointed by Phase II/III durability for anti-HER2 mAb Margenza margetuximab-cmkb from MacroGenics Inc. (NASDAQ:MGNX) in gastric cancer, which showed comparable efficacy to first-generation mAb Herceptin trastuzumab. The Fc-engineered anti-HER2 mAb plus anti-PD-1 mAb retifanlimab led to an ORR of 53% with 21 of 40 evaluable patients achieving an objective response in the interim analysis of the Phase II/III MAHOGANY study’s cohort A, including four complete responses. The company reported a 10.3 month duration of response and median PFS of 6.4 months.

Though MacroGenics was off 24% to $20.99 Thursday on the Margenza data, preliminary results from a Phase I study of MGC018 provide early proof of concept for the B7-H3-targeting ADC in castration-resistant prostate cancer. Among 39 patients treated with a median of three prior therapies, 21 (54%) achieved at least a 50% reduction in PSA levels and four of 16 patients evaluable for tumor response by RECIST had a partial response (25%). ...