Findings that suggest stem cells are at the root of colon cancer may lead to more effective treatments for the disease, and explain its tendency to recur.

Canadian and Italian researchers discovered the key role played by stem cells by implanting cells from human colorectal tumours in specially bred mice lacking an immune system.

John Dick found that a tiny number of cells in a tumour drives the growth of the cancer.
(CBC)

The researchers asked if every cell in a tumour has the same ability to keep cancer going. The answer they got was no.

It turns out only one in 60,000 cells — the stem cell — in the tumour actually has the ability to generate the cancer again, said Dr. John Dick, a senior scientist at the Ontario Cancer Institute at Princess Margaret Hospital in Toronto.

Driving force

"This cell could be swimming in a sea of chemotherapy agents and it would survive," Dick told CBC Newsworld on Monday. "So it would look like the tumour went away. But if these rare cells lurk about, they could actually start to regrow at later time points and could explain why we get such high rates of relapse for many different kinds of cancer."

Colon cancer stem cells are a driving force to sustain tumours, the researchers found.

"Since this is the heart of the tumour, you have to find and kill each of these colon cancer stem cells to truly cure the disease," Dick said.

Stem cells give rise to every type of organ and tissue in the body. No one knows where stem cells come from, although cancer stem cells are thought to act in a similar way to their benign cousins.

Similar experiments in Toronto have shown that leukemia stem cells can lie dormant for a long time.

The idea of cancer stem cells has circulated since the 1940s, but only in the last decade or so has technology advanced to allow scientists to find direct proof of their role, Dick said.

Knocking out the 'king' of cancer chess

The findings offer a test for cancer stem cells, said Alan Bernstein, president of the Canadian Institutes for Health Research in Ottawa, which helped to fund the research.

The next step is to study what makes the cancer stem cells unique and exploit that difference.

"If you want to win a chess game, you've got to knock off a lot of the pawns and knights," Bernstein said. "But at the end of the day, you've got to capture the king. So, I think we've got to focus on capturing the king."

In terms of treatment, the findings won't make a difference immediately, but hopefully they could in the next five to 10 years, Bernstein said. In the meantime, current treatments are the correct ones, targeting the bulk of the tumour, he said.

Future therapy target

The question is, do current chemotherapy regimes actually kill the cancer stem cell, said Mick Bhatia, who heads the stem cell and cancer research institute at McMaster University in Hamilton, Ont.

"I think obviously if they don't kill this particular cell, this tumor initiating cell, then we may need to come up with different combinations of therapy," said Bhatia, who was not involved in the research.

Both studies appear in Sunday's advance online issue of the journal Nature.

Colon cancer is the second most common cause of cancer-related death in Canada after lung cancer.

The Canadian Cancer Society estimated 20,000 men and women will be diagnosed with colorectal cancer this year in Canada, and 8,500 will die of the disease. It is the fourth most deadly cancer worldwide, according to the World Health Organization.

With files from the Canadian Press