In findings that could someday boost the cancer-killing ability of chemotherapy, New York researchers have a new theory on how tumors grow.
``Basically, for the last decade the prevailing theory has been that tumors feed into tissue and grow into a mass with no blood supply,'' explained Dr. George Yancopoulos, the chief scientific officer at Regeneron Pharmaceuticals in Tarrytown, N.Y.
The theory has been that in order to continue growing beyond just a few millimeters, the cancer sprouts new blood vessels to feed itself.
But in an article in the June 18 issue of Science, Yancopoulos and colleagues assert that much more occurs during the early stages of cancer growth.
``Really, there's a tremendous battle going on [between the body and the tumor],'' said Yancopoulos.
In experiments with several types of animal and human tumors, the researchers found that early on, tumors and healthy tissue vie for the same blood supply.
The tumors, said Yancopoulos, immediately attempt to ``abduct'' a tissue's blood vessels. ``But,'' he noted, ``the host doesn't idly sit by.''
Instead, a growth factor called angiopoietin-2 appears to send ``suicide signals'' to blood vessels abducted by tumors, the researchers found.
Several years ago, Yancopoulos and his colleagues discovered four types of angiopoietins, identifying their role in normal blood-vessel formation in embryos. The current findings are the first to show that angiopoietins may fight abnormal blood-vessel formation in tumors.
The body's ability to cut off this blood supply probably kills many infant-stage tumors, according to Yancopoulos. But some tumors save themselves with the help of another growth factor called vascular endothelial growth factor (VEGF). These ``successful'' tumors use VEGF to sprout new vessels, overwhelming the body's angiopoietin-2 defense, according to the New York researchers.
This VEGF-inspired comeback stage, Yancopoulos noted, is quite similar to what experts already believed that tumors eventually launch new blood vessels. His team's discovery of an early war between tumors and healthy tissue adds a new twist that could affect cancer treatment.
For instance, Yancopoulos said, when a cancer patient has a tumor removed, ``it's the tiny offshoots of the tumor the surgeon can't see that can come back to kill you.''
Researchers, he noted, are continually looking for ways to bolster the effectiveness of chemotherapy, which is used after surgery to help wipe out remaining tumors.
Drugs that help angiopoietin-2 head off these stray tumors could improve chemotherapy, Yancopoulos said. Already, there is a class of anti-VEGF drugs designed to block new vessel formation in leftover tumors.
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