FGFR3 and breast cancer: Given the potent antitumor activity of A2 but its off‐target toxicity in normal tissues such as the gastrointestinal tract and liver due to a lack of targeting ability, we designed and developed LZU‐WZLYCS01, a novel ADC targeting FGFR3, a BC‐specific antigen, with A2 as the cytotoxic payload (Figure5A).