Cancer Stem Cell. Cancer stem cells (CSCs) are a rare subset of cancer cells which have features such as the ability to self-renew, differentiate into defined progenies, and initiate and sustain tumor growth in vivo.Cancer Stem Cells (CSCs) are a small subpopulation of cells within tumors with capabilities of self-renewal, differentiation, and tumorigenicity when transplanted into an animal host. A number of cell surface markers such as CD44, CD24, and CD133 are often used to identify and enrich CSCs.Research has shown that cancer cells are not all the same. Within a malignant tumor or among the circulating cancerous cells of a leukemia, there can be a variety of types of cells. The stem cell theory of cancer proposes that among all cancerous cells, a few act as stem cells that reproduce themselves and sustain the cancer, much like normal stem cells normally renew and sustain our organs and tissues. In this view, cancer cells that are not stem cells can cause problems, but they cannot sustain an attack on our bodies over the long term.