The Preliminary Research On Biological Behaviors Of Breast Cancer Stem Cells From Different Molecular Subtypes

Objective: CD44⁺/CD24^–/low and aldehyde dehydrogenase-1（ALDH1） have been demonstrated as common markers for breast cancer stem cells（BCSCs） by lots of studies. Sorted tumor cell population bearing CD44⁺/CD24^–/low or ALDH1+phenotype can be used as models to study biological behaviors of BCSCs. Our study aims to compare distinctive biological behaviors between CD44⁺/CD24^–/low and ALDH1+ BCSCs and also to identify the biological behavior differentiation for BCSCs bearing the same phenotype among distinct breast cancer molecular subtypes.Methods: 1. We selected one case of fresh breast cancer tissues for each subtype from different subtypes of breast cancers as follows: Luminal A, Luminal B, HER-2 overexpression and Basal-like. CD44⁺/CD24^–/low and ALDH1-positive cell population were isolated from primary breast cancer cells by flow cytometry analysis. 2. The capacity of self-renewal of BCSCs was analyzed by mammospheres formation. 3. The NOD/SCID mouse model was used to observe the tumorigenicity capacity for BCSCs.Results: 1. The BCSCs bearing CD44⁺/CD24^–/low or ALDH1-positive phenotype within total tumor cells were accounted for 12.1% and 8.7% in Luminal A subtype, 2.7% and 5.7% in Luminal B subtype, 0.8% and 8.7% in HER-2 overexpression subtype, and 0.7% and 4.5% in Basal-like subtype, respectively. 2. Compared with CD44⁺/CD24^–/low BCSCs,the ALDH1-positive one formed more mammospheres in each molecular subtype（P<0.05）. Among breast cancer molecular subtypes, BCSCs bearing CD44⁺/CD24^–/low or ALDH1+ phenotype in HER-2 overexpression and Basal-like subtype formed more mammospheres than Luminal subtype（P<0.001）. 3. The sizes of transplantation tumors in NOD/SCID mouse injected with ALDH1+ phenotype cells were all larger than CD44⁺/CD24^–/low phenotype cells for all of these breast cancer subtypes, whatever Luminal B, HER-2 overexpression and Basal-like subtype（P<0.05）. Furthermore, it has also been detected that the size of transplantation tumors were significantly different among four breast cancer molecular subtypes（P<0.05）. The sizes of transplantation tumors in HER-2 overexpression and Basal-like were larger than Luminal subtype（P<0.001）. However, there were no obvious differences between HER-2 overexpression and Basal-like subtype. Likewise in Luminal A and B subtype（P>0.05）.Conclusion: 1.The CD44⁺/CD24^–/low or ALDH1-positive BCSCs have been successfully isolated from primary breast cancer cells. However, the proportion of BCSCs was significantly different among four breast cancer molecular subtypes. 2. BCSCs bearing different makers has different tumorigenesis and self-renewal capacity, that is ALDH1-positive one had stronger abilities than CD44⁺/CD24^–/low phenotype in Luminal B, HER-2 overexpression and Basal-like subtype. 3. Biological characteristics of BCSCs are significant different among different breast cancer molecular subtypes. The BCSCs of HER-2 overexpression and Basal-like subtype have stronger capacities of self-renewal and tumorigenesis than Luminal subtype.