The number of integrin β4+ CTCs expressing CD133 and ALDH1A1 stem markers but not CD44+CD24- was increased in metastatic breast cancer as well as in molecular subtypes of breast cancer with poor prognosis (luminal (HER2+) and TNBC) compared with luminal A/B (HER2−) subtype. Here, ALDH1A1 is linked to breast cancer.