Among the many mysteries of why some breast cancers prove more lethal than others, a protein called PIGU has emerged as a possible guide. Researchers publishing in Nature have found that PIGU is dramatically overexpressed in breast tumor tissue, reliably distinguishing cancer from healthy cells and correlating with significantly worse survival outcomes. Its presence appears to reshape the immune environment around tumors, suppressing the very cells that would otherwise mount a defense — a finding that places PIGU at the intersection of oncology and immunology, where the next generation of canc