Could Cancers Carry Their Own Stem Cells?
Stem cells contain the genetic source code for new healthy cells. And now three new studies, all published last week, seem to point to stem cells as the genetic source for some unhealthy cancerous tumors too. It is a disturbing idea that cancers may grow and re-grow out of their own stem cells.
The three studies looked at the brain, the skin and the gut and may prove to be a watershed in our understanding of the causes of cancer. The studies were published in the journals Nature and Science on Wednesday last week. All three groups of researchers marked and followed cellular progress from a restricted group of cells and found them to be the source of new tumor cells.
A team at the University of Texas South-western Medical Center looked into the regrowth of glioblastoma multiforme (GBM) tumors in the brain following chemotherapy. These brain cancer tumours are incurable at this time. They are aggressive with a median survival of around 1 and ¼ years. Even when the chemotherapy is successful to begin with, the cancer nearly always regrows. The researchers experimented on genetically modified mice to grow GBM tumors and saw ‘resting’ cells behaving like stem cells.
The tumors also contained unmarked cells that were destroyed by chemotherapy, but returned soon afterwards. When they analyzed them again, they identified the tumor cells had contained unmarked cells that came from marked source cells. The report’s lead author reported, “We identified a subset of brain tumor cells that are slower growing or remain at rest, and appear to be the source of cancer recurrence after standard therapy in which the drug temozolomide is given to stop the tumors’ growth.”
The skin cancer study was done in Belgium where scientists analyzed papilloma tumors. These can be the birthplace of skin cancers. Once again most of the tumor cells grew out of stem-like cells very similar to those that produce healthy skin cells. As with the GBM study they identified a clear sub section of cells promoting tumors. The more aggressive the tumor cells the more likely they were to give rise to ‘stem’ cells that go on reproducing. It is the current consensus that tumors only grow differentiated cells that can only reproduce a limited number of times.
The third study was of cells that grow intestinal tumors and was conducted in the Netherlands. The researchers ‘labelled’ normal gut cells so they could trace benign gut tumors that may turn into cancer. Again mice were given the genes that reacted to drugs and showed up in 4 colors. The tumors had numerous cell types but only one color suggesting they grew from a single stem cell.
What is exactly meant by the term ‘cancer stem cell’ is by no means certain and there is far from consensus on the idea among cancer researchers. But the 3 studies taken together do add a lot of credence to the idea of some cancer stem-like cells.