IDO1 and bladder transitional cell carcinoma: In this study, besides demonstrating that DAU can mediate the inhibition of macrophage M2 polarization and promote macrophage ferroptosis induced by BLCA cell supernatants via HCK, we further verified that DAU regulated IDO1, which is downstream of HCK, to affect the M2‐like TAMs induced by BLCA progression and ferroptosis.