Circulating tumor cells with a putative stem cell phenotype in peripheral blood of patients with breast cancer.

The CD44(+)/CD24(-/low) and ALDH1(+) cell phenotypes are associated with stemness and enhanced 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 with metastatic breast cancer using triple-marker immunofluorescence microscopy. Among a total 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 seven patients, were ALDH1(high)/CD24(-/low). In conclusion, we report the existence of a subpopulation of CTCs with putative stem cell progenitor phenotypes in patients with metastatic breast cancer.