In recent years, the theory of cancer stem cells has provided a new perspective on the treatment of cancers including breast cancer. The accurate sorting of breast cancer stem cells is critical. The sorting procedure is consist of 4 steps: isolation of side population, serum-free suspension culture,determination of specific cell surface markers and of the activity of aldehyde dehydrogenase 1 ( ALDH1 ) enzymatic through the ALDEFLUOR assay. Some studies choose drug resistance as an additional method for sorting cancer stem cells because of the enrichment of cancer stem cells after chemotherapy . The controversy about the sorting outcome of breast cancer stem cell mainly focus on molecular markers like CD44+ CD24- and ALDH1+ . The problem needed to be settled is to identify which sorting method and markers are appropriate.

Objective:The purpose of this study is to investigate the expression of tumor stem cell marker aldehyde dehydrogE-nase 1 (ALDH1) in breast cancer and its clinical significance. Methods:The expression of ALDH1 protein was examined by immunohistochemical staining in 92 breast cancer tissues. The correlation analysis and diseasE-free survival analysis of patients was evaluated based on the clinical follow-up data. Results:Expression of ALDH1 protein had a significant correlation with progesterone receptor (PR) and cerb-B2 (P<0.05), but had no significant correlation with age, tumor size, clinical staging, and lymph node metastasis (P>0.05). The 2-year diseasE-free survival rate of AlDH1-positive patients was lower than that of ALDH1-negative patients (P<0.05). ALDH1-positive patients, who received CEF regimen chemotherapy and hormone therapy, had lower 2-year diseasE-free survival rate than that of ALDH1-negative patients (P<0.05). Conclusion:The decreased diseasE-free survival rate of ALDH1-positive patients is related with drug resistance. ALDH1 could be used as an independent factor for predicting the prognosis of breast cancer.