Canadian scientists say they have evidence that shows colon cancer arises from stem cells specific to the tumor, a finding that could lead to more targeted treatments to prevent recurrence of the disease.

The discovery was made after cells from human colorectal tumors were implanted in specially bred mice, said principal investigator Dr. John Dick, a senior scientist at the Ontario Cancer Institute at Princess Margaret Hospital in Toronto.

Dick's research was published Sunday in an advance online edition of the journal Nature.

"We found that not every tumor cell is equally capable of sustaining tumors in the colon," said Dick, who holds a Canada research chair in stem cell biology. "Colon cancer stem cells are the driving force initiating and sustaining these tumors."

Stem cells are the building blocks of the body from conception, giving rise to every type of organ and tissue. Although it is not known when or from where they originate, cancer stem cells act in a similar fashion to their benign cousins, providing the foundation for at least some malignancies.

To see if stem cells were at the root of colorectal cancer, Dick's team began by taking samples of tumors surgically removed from patients' large intestines or other areas of the body where the cancer had spread. They broke the tumors down into individual cells, then implanted "millions and millions" of them into the capsule surrounding the kidney of each laboratory mouse.

In all, 17 mice were implanted - and all 17 developed tumors, said Dick, explaining that the immune-deficient mice lack disease-fighting cells, so cancer can grow unchecked.

Through painstaking work transplanting various numbers of tumor cells into mice, the scientists initially determined that colon cancer stem cells are rare - occurring at a rate of about one in 60,000 cells.

They then narrowed the search even further by testing the cells for the presence or absence of CD133, a protein on the surface of some cells, which has been implicated in some other types of cancer, among them brain and breast.

The researchers also found that the new tumors were comprised of both positive and negative CD133 cells, proving that both types originated from the initial transplanted cell.

Based on this discovery, scientists can now begin to identify unique genetic properties of colon cancer stem cells and then develop drugs targeting these characteristics to prevent the disease from recurring.

Colorectal cancer is the second most deadly malignancy among Canadians after lung cancer, Canadian Cancer Society figures show. An estimated 20,000 men and women will be diagnosed with colorectal cancer this year, and 8,500 will die of the disease.