Tumor Starters: Stem Cells Eyed as Anti-Cancer Target

Nov. 24, 2006 — -- Decades of cancer research may need to be re-evaluated, because standard tumor-targeting therapies may be off the mark, mounting research suggests.

Current cancer therapies attack tumors as if every cell in that tumor were the same. But now, scientific evidence suggests that only a small percentage of those tumor cells are responsible for the tumor's growth. Treatments that attack the whole tumor may be off target because they aren't designed to kill the cells at fault -- stem cells.

Called the cancer stem-cell hypothesis, it could revolutionize the way some cancers are treated, experts said.

"The cancer stem-cell theory solves several unanswered questions," said Dr. Raphael Catane, chairman of the department of oncology at Sheba Medical Center in Israel.

Stem cells have an unbeatable potential to develop into many different cell types in the body. While an adult skin cell can duplicate only more skin cells, a stem cell's cellular future is less restricted.

But that future isn't always bright. Abnormal stem cells are responsible for cancers of the blood, breast, brain, bone and prostate, according to past research.

Now, scientists from Canada and Italy report that colon cancer is also caused by abnormal stem cells. The report appears in this week's issue of the journal Nature. The evidence keeps mounting.

Stem cells, specifically embryonic stem cells, also have an unmatched potential for generating controversy. Usually, those cells spark ethical debates about when life begins, so to speak, or whether embryonic stem cell research destroys life by using cells from discarded embryos.

Cancer stem cells are not embryonic stem cells but are derived from adult tissue. Nevertheless, it's possible that scientists may seek to use embryonic stem cells as part of their cancer stem-cell research.

Researchers are now convinced that cancer stem cells -- which make up only a tiny fraction of a tumor -- produce the other tumor cells that make up the bulk of the cancer. The stem cells react very differently to chemotherapy drugs or other cancer treatments than the tumor cells do, said Dr. Grover Bagby, director of the Oregon Health and Sciences University Cancer Institute in Portland, Ore.