SERPINE1 and breast cancer: As a critical control comparison, we also examined the effects of PAI1 and HER2 kinase combination therapy on fibroblast viability and found lower reduction in cell viability compared to breast cancer cells (Fig. 2D: 27% reduction in fibroblast viability in 20 μM tiplaxtinin combined with 1 μM lapatinib compared to a range of 30% to 89% reduction in cancer cells cocultured with fibroblasts).