UCSF scientists discovered extracellular membrane‑associated Src (eSrc) on the surface of multiple tumor types and demonstrated that antibodies targeting eSrc shrink tumors in mouse models, the group reported in Science. The team showed that autophagolysosomal exocytosis flips intracellular Src to the cell surface in cancer cells overwhelmed by protein‑recycling stress. The finding converts a long‑studied intracellular oncogene into a potential antibody or antibody‑drug conjugate target across multiple solid tumors. Translational teams will need to develop clinical‑grade binders, confirm tumor specificity in human tissues, and assess safety because Src is essential in normal cell signaling. If validated clinically, eSrc could broaden immunotherapy antigen space for hard‑to‑treat cancers.