We apply MiXcan to conduct the first cell-type-aware TWAS of breast cancer risk in 31,716 cases and 26,932 controls, and report three new susceptibility genes (ZNF703, TMEM245, and PSG4) with evidence of distinct associations in mammary epithelial versus stromal cells that were not detected by prior TWAS nor GWAS. Here, PSG4 is linked to breast carcinoma.