Research carried out by scientists in Canada has found that the protein p110g suppresses colorectal cancer - cancers of the bowel and rectum.
The scientists came across the discovery by accident.
Even if people have diverse mutations which predispose to colorectal cancer, our protein might have the possibility to shut them all down
Professor Josef Penninger
They were not trying to see how it affects cancer cells. In fact, scientists had previously suggested that the protein could itself cause cancer.
Professor Josef Penninger, from the University of Toronto, said the results were unexpected.
"We were studying mice that were genetically engineered to lack the protein and they started to get very sick and die.
"Soon we found they had invasive colorectal cancer. We never, ever would have expected that because every prediction about p110g had been that it actually caused cancer."
Following that initial discovery, the research team tested the theory on human colorectal cancer cells taken from patients' tissue.
They found no evidence of the protein in approximately one in four of the colorectal cancer samples.
Bowel cancer facts
It is the third most common cancer in UK men
Bowel cancer is the second most common cancer in UK women
16,477 new cases in men emerged in 1995
The figure for women was 15,742
"This is very hopeful because it means even if people have diverse mutations which predispose to colorectal cancer, our protein might have the possibility to shut them all down," said Prof Penninger.
The researchers then injected human colorectal cancer cells into normal mice. The mice quickly grew tumours.
But the scientists then added the protein to the cancer cells and discovered that again the spread of colon cancer was stopped.
"These results are a good argument that this is the real thing and it is strong evidence for the protein's role in humans," said Prof Penninger.
The research team is now looking to examine the exact workings of the protein in colorectal cancer.
This could lead to future drug therapies that replicate or stimulate the protein's action in stopping tumour growth.
Researchers will also investigate whether some people have a genetic mutation that causes them to not have the protein and therefore be predisposed to colorectal cancer.
The research is published in the latest issue of the journal Nature.
A spokeswoman for the Cancer Research Campaign in the UK welcomed the study.
Bowel cancer is the third most common cancer in men, and the second most common cancer in women in the UK.
In 1995, there were 16,477 new cases of bowel cancer recorded in men, and 15,742 cases in women.