Defining Stem Cells
What are stem cells?
Every organ and type of tissue in the body contains a small number of what scientists call "adult" or "tissue" stem cells. Since most cells in the body live for just a short time, the body needs to keep making new cells to replace them. Adult stem cells ensure a continuous supply of new cells to replace old cells that wear out or are destroyed.
Stem cells have properties that make them different from ordinary cells.
- They divide
Stem cells can divide to make exact copies of themselves - a property scientists call self-renewal.
- They differentiate
Stem cells can differentiate to make specialized cells called progenitor cells that go on to form the organs and tissues in the human body.
- They duplicate
Every time a stem cell divides, it makes one exact copy and one progenitor cell. When the progenitor cell divides, it produces two cells that are somewhat more specialized. Each generation of new cells is more specialized than the previous generation until, eventually, mature cells are produced.
- They divide indefinitely
Many cells can divide to make copies of themselves, but they can only divide a certain number of times before they die. Stem cells can keep dividing indefinitely. Because stem cells are essentially immortal, the body keeps them under tight control, so they will divide only when a new supply of cells is needed.
What types of stem cells were discovered at the U-M Cancer Center?
In 2003, U-M scientists were the first in the world to identify cancer stem cells in a solid tumor, finding them in breast tumors. Since then, other Cancer Center scientists have discovered and isolated cancer stem cells in pancreatic cancer (2007), in head and neck cancer (2007) and in an aggressive brain cancer called glioblastoma (2009).