ERBB2 and neoplasm: Similar delayed responses have been noted in patients treated with other PE immunotoxins targeting antigens like mesothelin (SS1P), EpCAM (VB4‐845), and HER2 (scFv (FRP5)‐ETA).[24] These observations are reminiscent of patterns seen with immune checkpoint inhibitors,[25] suggesting a potential role for immunotoxins in stimulating anti‐tumor immunity.