Van Keymeulen, et al. showed in the mouse that basal cells (as determined by keratin expression) can adopt a multipotent progenitor fate and completely recapitulate the mammary gland upon transplantation, suggesting a possible mechanism by which the triple negative human breast cancer cells used here might generate mammary gland outgrowths containing hK8-expressing luminal cells [36]. This evidence concerns the gene KLK8 and breast cancer.