ALDH1A1 and breast cancer: Assuming that metastasis requires a dissemination of tumor stem cells or tumor cells showing EMT, we studied the expression of (1) the EMT markers Akt2, phosphoinositide kinase-3α (PI3K-α) and the transcription factor TWIST1 and (2) the stem cell marker ALDH1 in CTC isolated from 502 patients with primary breast cancer.