CancerQuest | What are Cancer Stem Cells

What is a stem cell?

A stem cell is a special cell type that has both the ability to reproduce exact copies of itself (also called self-renewal) and the ability to change (differentiate) into one of the many specialized cell types in the body. Examples of specialized cells that arise from stem cells include nerves, muscles and the cells lining our digestive system. In most parts of the body, stem cells are not very active. In some locations, including the gastrointestinal tract, stem cells divide and differentiate constantly to replace cells that are shed or die. Stem cells are also important during healing of damaged tissues. Below is a video of the process by which stem cells can accomplish both self-renewal and differentiation. The process is called asymmetric cell division and it assures that stem cells are always available when needed.⁽¹⁾

What is a cancer stem cell?

Cancer stem cells are thought to arise from normal stem cells. Normal stem cells become damaged by mutation and no longer function properly. A main difference between normal stem cells and CSC is that CSC have uncontrolled reproduction and may form tumors. The existence of CSCs was predicted decades ago, but recent research has identified cancer stem cells in multiple cancer types prompting large amounts of research in this field.⁽¹⁾⁽²⁾

Where do cancer stem cells come from?

In theory, CSCs could be formed in more than one way. Mutations could occur in a differentiated cell (i.e. a skin cell) causing the cell to go backwards or 'devolve' into a cell with some stem cell abilities. Cancer stem cells could also be formed by the mutation of a normal stem cell that causes it to become cancerous. Cancer stem cells have been created in research laboratories from skin cells⁽³⁾ The researchers used a virus to activate specific pathways and give the target cell stem cell-like qualities. The research proves that a normal cell can become a stem cell with the right set of mutations.

The probability of any particular cell developing a set of mutations that leads to cancer is relatively low. The cells types that are affected by the majority of cancers, epithelial cells, have short lives and are even less likely to accumulate all the mutations they need. Normal stem cells, which are long-lived, are more likely to be around long enough to accumulate the necessary mutations and are a good possible source of cancer stem cells.⁽¹⁾

Learn more about genetic change (mutation).

What is the difference between the cancer stem cell hypothesis of the origin of cancer and traditional views on the origin of cancer?

The cancer stem cell hypothesis suggests that only a small portion of cells are capable of becoming cancerous. A second prediction is that only a small population of cells in a tumor is responsible for the continuous, uncontrolled growth seen in cancer. The traditional views on the origin of cancer predict that any cell is able to acquire mutations that lead to uncontrolled reproduction. Likewise, all of the cells in a tumor would be predicted to be able to divide endlessly.⁽²⁾