ALDH1 expression level and ratio of tumor cells CD44+CD24low, CD326+CD44+CD24−, CD326−CD49f+, CSC of mesenchymal origin (CD44+CD24−) and epithelial tumor cells (CD227+CD44+CD24− and CD44+CD24−CD49f+), HSC, and CD309+ endothelial cells in tumors can act as personalized diagnostic markers, predictors of complications and the effectiveness of breast cancer treatment in further research. This evidence concerns the gene MUC1 and breast cancer.