Cancer stem cells in solid tumors

Carcinogenesis and tumor cell biology are very complex subjects. Recent findings on cancer stem cells may have a great impact on the understanding of the biology of malignancies and the development of future treatment approaches. Cancer stem cells are defined by their potential to self-renew and differentiate. Identification of cancer stem cells is possible by detecting expression of a certain combination of various cell surface markers and also by functional assays. The cancer stem cell concept was originally developed for hematological malignancies but is now becoming accepted for solid tumors as well. Emerging data indicates that cancer stem cells are responsible for the growth and spread of tumors. There is still a long way to go in characterizing cancer stem cells and understanding their role in carcinogenesis. Further studies should lead to a greater understanding of the biology of these cells with significant implications for diagnosis, treatment, and prevention of cancer. The recent studies regarding stem cell origin of various solid tumors will be discussed briefly in this review.