The other half of the time, some tumor cells survive treatment. These cancer cells are more aggressive than they were before treatment, says Mark W. Dewhirst, DVM, PhD, professor of radiation oncology at Duke University.
"When you give a tumor treatment, whatever cells survive are going to be more resistant to that treatment," Dewhirst tells WebMD. "Those not killed are healthier cancer cells."
This does not mean radiation and chemotherapy don't work. It does mean that additional new treatments will be needed. And to know what treatments will work best, Dewhirst says doctors need to know how cancer cells survive radiation and chemotherapy.
The key may be a protein called HIF -- hypoxia-inducing factor. Government, university, and drug-company researchers are racing to develop new drugs that inhibit HIF. But patients may not have to wait that long: Existing drugs, already approved by the FDA for cancer treatment, turn out to be potent anti-HIF agents.
Why is HIF suddenly a big deal? It's the key to a different way of looking at cancers.
A 'New' Theory of Cancer
It's been known for about 50 years that solid tumors have areas that don't get much blood -- and that cells in these areas survive without much oxygen.
For a long time, this was thought to be an interesting curiosity. But now the ability of cancer cells to survive without oxygen -- to become hypoxic -- is being seen as a driver of cancer progression.
"A cancer cell that doesn't get much oxygen is like a rat deserting a sinking ship," Dewhirst says. "It will do things to try to help itself."
So the cell does four things:
It sends out a signal for help, asking the body to grow more blood vessels in the tumor.