Objective To investigate the expressions and clinical significances of breast cancer stem cell markers such as aldehyde dehydrogenase 1 (ALDH1) and transforming growth factor-β2 (TGF-β2) in patients with triple negative breast cancer.Methods Samples of 60 triple negative breast cancer tissues were investigated for the expressions of ALDH1 and TGF-β2 proteins by immunohistochemical staining.The correlation analysis,disease-free survival analysis and overall survival analysis were performed.Results The positive expressions of ALDH1 protein and TGF-β2 protein in the 60 breast cancer primary lesions were 23 cases (38.33％) and 38 cases (63.33％) respectively.The expression of ALDH1 protein was not correlated with tumor size (x2 =0.307,P =0.580),histological grade (x2 =4.244,P =0.120),clinical stage (x2 =0.982,P =0.612) or lymph node metastasis (x2 =1.111,P =0.292).The expression of TGF-β2 protein was not correlated with histological grade (x2 =4.651,P =0.098),lymph node metastasis (x2 =3.513,P =0.061),clinical stage (x2 =1.310,P =0.519) or tumor size (x2 =0.629,P =0.428).The disease-free survival time [(38.43±3.86) months vs.(53.38 ±2.58) months] and the overall survival time [(42.00±3.11) months vs.(53.84 ± 2.19) months] of ALDH1-positive patients were significantly shorter than those of ALDH1-negative patients,and the differences were statistically significant (x2 =8.490,P =0.004;x2 =11.270,P =0.001).The disease-free survival time [(42.81 ±3.32) months vs.(54.72 ±2.50) months] and the overall survival time [(44.74 ± 2.68) months vs.(57.18 ± 1.55) months] of TGF-β2 positive patients were significantly shorter than those of TGF-β2-negative patients,and the differences were statistically significant (x2 =4.300,P =0.038;x2 =8.900,P =0.003).The expression of ALDH1 protein was positively correlated with the expression of TGF-32 protein (r =0.360,P =0.005).Conclusion The ALDH1 phenotype is an independent predictor of poor prognosis.The activation of TGF-32 signaling pathway may be involved in the regulation of triple-negative breast cancer stem cells.