When cancers are treated, tumors may shrink but then come roaring back. Now studies on three different types of tumors suggest a key reason why: The cancers are fueled by stem cells that chemotherapy drugs don't kill.
The findings — made by independent research teams that used mice to study tumors of the brain, intestines and skin — could change the approach to fighting cancers in humans, experts said.
Properties of these so-called cancer stem cells can be investigated so researchers can devise strategies for killing them off, said Luis F. Parada, a molecular geneticist at the University of Texas Southwestern Medical Center in Dallas and senior author of one of the studies published Wednesday.
"Everything has a soft underbelly once you understand it well," Parada said. "With all the modern molecular techniques and modern approaches we have, we should be able to find their soft underbelly."
Cancer researchers have long suspected — and some pioneering studies have strongly suggested — that specific cells within tumors are responsible for their continued growth. But the earlier experiments hadn't convinced everyone, and the hypothesis has been controversial.
The three papers published by the journals Nature and Science "really should seal the deal," said cancer biologist Owen Witte, director of the Broad Stem Cell Research Center at UCLA.
"People can stop arguing," he said. "Now they can say, 'OK, the cells are here. We now need to know how to treat them.' "
All three studies used molecular tricks that allowed scientists to mark certain tumor cells with bright colors. When these marked cells divided, all of the daughter cells were similarly colored. This permitted the researchers to see whether any old cell in a tumor can continue to fuel its growth or if only a subset of cells is responsible.