Among CTC identified in patients with metastatic breast cancer, 32% had the stem cell like phenotype CD44+CD24- and 17% of the CTC were positive for one other recently proposed stem cell marker, aldehyde dehydrogenase 1 (ALDH1) [13] which has been associated with poor prognosis in different forms of breast cancer [14,15]. The gene discussed is ALDH1A1; the disease is breast cancer.