Stem Cells May Be at Root of Cancer
New Research May Explain Why So Many Tumor-Fighting Treatments Now Fail
WebMD News Archive
A New Model for Cancer continued...
"In this theory, any cell that gets the right series of mutations can
become cancer," he says.
In the stem cell hypothesis, cancer is driven by specific cells that contain
stem cell properties, Wicha says. These cells then reproduce and replenish
Currently, most treatments target cancer cells, but not necessarily cancer
stem cells, he says. While the treatment may shrink the tumor and keep it in
check for a while, eventually, the untreated cancer stem cells proliferate into
cancer cells, leading to a return of the tumor and death, he says.
If the treatments targeted the cancer stem cells, however, the tumor would
lose the ability to generate new cancer cells, eventually resulting in a cure,
Think dandelions, says researcher Peter Chu, PhD, of Biogen Idec in San
Diego. "If you cut a weed and don't get the root, it will grow back,"
he tells WebMD. "So if you don't [kill off] cancer stem cells, you're not
going to see better long-term survival."
Wicha notes that the concept that stem cells cause cancer is not new. But
recent advances in molecular biology -- such as the development of tests that
allow researchers to locate and measure the cancer stem cells -- are giving it
new credibility, he says.
Stem Cells Drive Aggressive Breast Tumors
Experiments in Wicha's lab show that two genes, PTEN and HER2/neu, that are
associated with aggressive breast cancers have stem cell properties. Defects in
either gene are tied to faster-growing tumors that are more likely to
The researchers studied three types of genetically altered breast cancer
cells: One had the PTEN defect, one had the HER2/neu defect, and one had both
Results showed that that either defect increases the stem cell population by
two to five times. Furthermore, there was an approximately tenfold increase in
the stem cell population when they created a cell line with both PTEN and
Then, the researchers injected the three types of genetically altered cells
into mice. Cells with either defect induced the growth of tumors that were
four to six times more aggressive than normal. Injection of the cells with
both alterations caused tumors that were 10 times more aggressive.
Wicha believes the experiments may help explain why Herceptin, the biologic
therapy that targets the HER2 protein on cancer cells, works so well.
"We believe that knocking out the tumor-causing cancer stem cells
explains why Herceptin reduces that chance of cancer coming back by 50% [in
women with HER2 positive breast cancer], although that remains to be
proven," he says.