A method for enriching a population of somatic mammary stem cells or
mammary tumor stem cells based on low-density lipoprotein
receptor-related protein 6 (LRP6). Also included are methods for
screening for LRP6 modulators, as well as methods for reducing Wnt
signaling, for treating Wnt signaling-related diseases, for detecting
mammary basal-like cells, for diagnosing basal-like breast cancer, and
for inhibiting proliferation of a tumor expressing LRP6, and compositions
thereof.