Wendy A. Woodward, MD, PhD

Breast cancer has long been described as a very heterogeneous disease, and clinicians have struggled with identifying the appropriate treatment program for an individual patient on the basis of multiple variables, including histology, nuclear grade, tumor size, nodal status, hormone receptor status, and a variety of prognostic factors.

The publication of the landmark paper by Al-Hajj et al, which demonstrated that breast cancer cells capable of tumor outgrowth when transplanted into the cleared mammary fatpad of immunocompromised mice could be prospectively identified using cell surface markers,[1] galvanized the cancer stem cell debate among breast cancer researchers and launched an exponential increase in papers exploring “breast cancer stem cells.”