APOA4 and cancer: Combined with label‐free and MRM quantification, a total of 10 urinary proteins (HPT, APOA4, CO4, B2MG, A1AG, CATC, VCAM1, CALB1, CSPG4, and VTDB) changed significantly even before a tumor mass was palpable, and these early changes in urine also showed differential abundance at late stages of cancer.