Breast cancer is a progressive and potentially fatal disease that affects women 
of all ages. Like all progressive diseases, early and reliable diagnosis is the 
key for successful treatment and annihilation. Biomarkers serve as indicators of 
pathological, physiological, or pharmacological processes. Her2/neu, CA15.3, 
estrogen receptor (ER), progesterone receptor (PR), and cytokeratins are 
biomarkers that have been approved by the Food and Drug Administration for 
disease diagnosis, prognosis, and therapy selection. The structural and 
functional complexity of protein biomarkers and the heterogeneity of the breast 
cancer pathology present challenges to the scientific community. Here we review 
estrogen receptor-related putative breast cancer biomarkers, including those of 
putative breast cancer stem cells, a minor population of estrogen receptor 
negative tumor cells that retain the stem cell property of self-renewal. We also 
review a few promising cytoskeleton targets for ER alpha negative breast cancer.