By integrating large-scale protein quantitative trait loci (pQTL) data from two major cohorts (DeCODE and UK Biobank) with BC genetic association data from three independent sources (FinnGen, BCAC), the analysis identified four proteins-intestinal alkaline phosphatase (ALPI), coiled-coil domain containing 134 (CCDC134), cadherin 1 (CDH1), and ST3 beta-galactoside alpha-2,3-sialyltransferase 2 (ST3GAL2)-with levels associated with a significantly reduced risk of BC. Here, CCDC134 is linked to breast cancer.