ERBB3 and cancer: Collectively, we demonstrated HER3 specific accumulation of [89Zr]Mab#58 in vivo and the potential of [89Zr]Mab#58 as a PET probe for non-invasive HER3 imaging not only in cancer cell line transplant model but also in more biologically and clinically relevant CTOS transplant models, in which the critical role of HER3 signaling was revealed.