Identifying Circulating Tumor Stem Cells That Matter: The Key to Prognostication and Therapeutic Targeting

Abstract

TO THEEDITOR: We read with interest the article by Iinuma et al 1 that describes their study examining the clinical significance of cancer stem cells in the peripheral blood of patients with colorectal cancer (CRC). The defining characteristics of a circulating cancer stem cell (CTSC) are its capacity for self-renewal and for initiation of distant metastases; some of these cells are also resistant to traditional chemo- therapy. 2,3 The concept that circulating tumor stem cells can be iden- tified and targeted is attractive and has major diagnostic, prognostic, and therapeutic implications for patients with metastatic cancer. However, the identification of authentic CTSCs continues to be a challenge because of the lack of a clear understanding of the biologic heterogeneity of tumor stem-cell populations and also because of the lack of characterization of surface markers that predict clinically im- portant subsets of CTSCs, such as those with aggressive malignant potential or drug resistance.