Researchers pinpoint colon cancer stem cells

WASHINGTON, June 5 (Reuters) A small population of stem cells drives tumor growth in colon cancer, researchers said in a discovery that could lead to a new approach to tackle the deadly disease.

This is the latest form of cancer for which researchers have pinpointed stem cells that propagate tumors. Others include cancers of the breast, brain, pancreas and blood cells.

Colon cancer, sometimes called colorectal cancer, arises in the large intestine or rectum and is a leading cause of cancer deaths.

Nearly all cases start as benign polyps that over time develop into cancer.

''Within a tumor, not all tumor cells are created equal,'' Dr Piero Dalerba of Stanford University School of Medicine in California, one of the researchers, said in a telephone interview yesterday.

''There is a tiny minority population of cells that is very dangerous and has special properties that are different from the majority of tumor cells in the tumor mass,'' Dalerba added. ''The implication of this is that when you try to treat a tumor, you have to target this population of cells.'' He expressed hope that the finding, published in the Proceedings of the National Academy of Sciences, would lead to treatments to wipe out these cells and eradicate the cancer.

The discovery in recent years of stem cells responsible for driving tumor growth has prompted an important change in the understanding of the biology of cancer.

These cells perpetually divide to produce new tumor cells, fueling tumor growth, and also may be the culprits when tumors spread to other parts of the body, the researchers said. Ordinary tumor cells can divide and cause damage, but are shorter-lived and cannot maintain tumor growth, they said.

''Maybe an effective treatment does not necessarily induce a rapid regression of a tumor, but could slowly exhaust its growth potential. If it basically kills this small population of cells, the total mass would not be effected (immediately) but its growth over time, yes,'' Dalerba added.

The research highlighted the role of a protein called CD44 found in colon cancer stem cells that was found previously in breast, head and neck cancer stem cells. The researchers also found a protein in colon stem cells called CD166 that they said could serve as a target for new treatments.

The American Cancer Society estimates that colorectal cancer will kill about 52,000 people in the United States this year. The organization said the colon death rate has been declining for the past 15 years in part because more people are getting tests that can reveal polyps so they can be removed before they can turn cancerous.

REUTERS DS BD0853