KLK6 and breast cancer: We have previously shown that kinin B1R favors the malignant phenotype of breast cancer cells (MCF-7, T47D, and ZR-75-1 cells) because its stimulation by B1R agonists induces cell proliferation and secretion of metalloproteinases-2 and -9, and of kallikrein-related peptidase 6, among other effects (6, 29, 49).