CD44 or CD24 expression alone does not classify breast cancer cell lines into tumor subytpes. Breast cancer cell lines are grouped based on tumor subtype classification defined by  as Luminal, Basal A (Bas A), Basal B (Bas B), or those that have not been previously classified (NC). The percentage of cells in breast cancer cell lines expressing either CD44 (a) or CD24 (b) is variable and does not correlate with tumor classification. (c) The percentage of cells in cancer cell lines expressing the CD44+/CD24- phenotype correlates with spindle/mesenchymal features, not tumor subtype. Surface marker expression was quantified by flow cytometry (mean ± S.E.) as described in Materials and methods. Phase contrast, bright-field photomicrographs of representative cell lines exhibiting epithelial versus spindle morphology.