Wnt signaling, stem cells, and the cellular origin of breast cancer

Stem Cell Rev. 2007 Jun;3(2):157-68. doi: 10.1007/s12015-007-0025-3.


The breast epithelium comprises cells at different stages of differentiation, including stem cells, progenitor cells, and more differentiated epithelial and myoepithelial cells. Wnt signaling plays a critical role in regulating stem/progenitor cells in the mammary gland as well as other tissue compartments. Furthermore, there is strong evidence suggesting that aberrant activation of Wnt signaling induces mammary tumors from stem/progenitor cells, and that Wnt exerts its oncogenic effects through LRP5/6-mediated activation of beta-catenin and mTOR pathways. Recent studies using avian retrovirus-mediated introduction of oncogenes into a small subset of somatic mammary cells suggest that polyoma middle T antigen (PyMT) may also preferentially transform stem/progenitor cells. These observations suggest that stem/progenitor cells in the mammary gland may be especially susceptible to oncogenic transformation. Whether more differentiated cells may also be transformed by particular oncogenes is actively debated; it is presently unclear whether stem cells or differentiated mammary cells are more susceptible to transformation by individual oncogenes. Better stem cell and progenitor cell markers as well as the ability to specifically target oncogenes into different mammary cell types will be needed to determine the spectrum of oncogene transformation for stem cells versus more differentiated cells.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Review

MeSH terms

  • Animals
  • Antigens, Polyomavirus Transforming / metabolism
  • Biomarkers, Tumor / metabolism*
  • Breast Neoplasms / metabolism*
  • Breast Neoplasms / pathology
  • Cell Differentiation
  • Cell Transformation, Neoplastic
  • Epithelial Cells / metabolism
  • Epithelial Cells / pathology
  • Female
  • Humans
  • LDL-Receptor Related Proteins / metabolism
  • Low Density Lipoprotein Receptor-Related Protein-5
  • Low Density Lipoprotein Receptor-Related Protein-6
  • Mammary Glands, Animal / metabolism
  • Mammary Glands, Animal / pathology
  • Mammary Glands, Human / metabolism*
  • Mammary Glands, Human / pathology
  • Mammary Neoplasms, Animal / metabolism
  • Mammary Neoplasms, Animal / pathology
  • Neoplastic Stem Cells / metabolism*
  • Neoplastic Stem Cells / pathology
  • Protein Kinases / metabolism
  • Signal Transduction*
  • TOR Serine-Threonine Kinases
  • Wnt Proteins / metabolism*
  • beta Catenin / metabolism


  • Antigens, Polyomavirus Transforming
  • Biomarkers, Tumor
  • LDL-Receptor Related Proteins
  • LRP5 protein, human
  • LRP6 protein, human
  • Low Density Lipoprotein Receptor-Related Protein-5
  • Low Density Lipoprotein Receptor-Related Protein-6
  • Wnt Proteins
  • beta Catenin
  • Protein Kinases
  • MTOR protein, human
  • TOR Serine-Threonine Kinases