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Their findings may help scientists develop new cancer treatments that harness the immune system's cancer-fighting powers.
Here's an overview of the studies, published in today's advance online editions of Nature and Proceedings of the National Academy of Sciences.
In Nature, scientists show that a healthy immune system may hold some cancers in check.
The results may pave the way for the development of new therapies to "convert cancer into a controllable chronic disease," write the researchers.
They injected a cancer-causing substance into mice. Some mice developed growing tumors, while other mice developed tumors that stayed small.
But those small, stable tumors started to grow when the scientists suppressed the mice's immune systems.
The bottom line: A healthy immune system helps prevent cancer, though it didn't stop every small tumor from growing.
The researchers included graduate student Catherine Koebel and Robert Schreiber, PhD, of the pathology and immunology department at Washington University School of Medicine in St. Louis.
Their findings are "startling" and "demonstrate that considering cancer as a fatal disease is not always appropriate," writes Cornelius Melief, MD, PhD, in a Nature editorial.
Melief works at Leiden University in the Netherlands.
Cancer Defies Immune System
Sometimes, cancer flies under the immune system's radar, a British study shows.
The study focuses on immune system cells called regulatory T-cells (T-regs) and their effect on macrophages in test tubes.
Macrophages normally help the body get rid of threats. But under the sway of T-regs, macrophages act the opposite way. Instead of going on defense, the macrophages chill out, as if there were no cause for concern.
That process could open the door for tumor growth, note the researchers, who included Leonie Taams, PhD, of King's College London.
"We hope to be able to use this new knowledge about the relationship between regulatory T-cells and macrophages to find more effective treatments for tumors," Taams says in a news release.
SOURCES: Koebel, C. Nature, Nov. 18, 2007; advance online edition. Melief, C. Nature, Nov. 18. 2007; advance online edition. Tiemessen, M. Proceedings of the National Academy of Sciences, week of Nov. 19-23, 2007; advance online edition. News release, Washington University School of Medicine. News release, Biotechnology and Biological Sciences Research Council.
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