The CD44+/CD24/low and ALDH1+ cell phenotypes are associated with stemness andenhanced tumorigenic potential in breast cancer. We assessed the expression of CD44,CD24 and ALDH1 on tumor cells circulating in the peripheral blood (CTCs) of patients withmetastatic breast cancer using triple-marker immunofluorescence microscopy. Among atotal of 1439 CTCs identified in 20 (66.7%) out of 30 patients, 35.2% had the stem-like/tumorigenic phenotype CD44+/CD24/low, whereas 17.7% of the CTCs analyzed in sevenpatients, were ALDH1high/CD24/low. In conclusion, we report the existence of a subpopulationof CTCs with putative stem cell progenitor phenotypes in patients with metastaticbreast cancer.