Differentially expressed proteins were analyzed to construct a diagnostic model, which was validated in an independent cohort (111 breast cancer patients [56 early-stage, 55 late-stage] vs. 95 healthy controls).<h4>Results</h4>The combination of INPP1 (first reported as downregulated in breast cancer serum) and ARHGAP25 demonstrated high diagnostic accuracy, achieving AUCs of 0.8458 (discovery cohort) and 0.8506 (validation cohort). Here, INPP1 is linked to breast cancer.