Discussion

FS102 is a HER2 specific Fcab™ (Fc fragment with antigen binding) which recognises an epitope that does not overlap with those of trastuzumab or pertuzumab. In tumour cells expressing high HER2 levels, FS102 induced profound HER2 degradation and potent cell apoptosis. The anti-tumour effect of FS102 in patient-derived xenograft (PDX) models correlated strongly with HER2 amplification status and was superior over trastuzumab when tested in a biomarker-positive subset of PDX. We hypothesise that the unique structure of FS102 leads to greater depletion of the receptor which commits the HER2-addicted tumour cells to apoptosis.