Scott LaFee, Contributor
HUMAN STEM cells boast a kind of immortality. They are able to precisely copy themselves, over and over, for our entire lives. We shed and regrow our outer layer of skin cells once every 27 days or so - roughly 1,000 new skins in the average lifetime.
But the stem cells from which those outer skin cells originate are essentially the same ones we were born with - and the same ones with which we die. It's this enduring quality, combined with their remarkable ability to develop into almost any kind of cell needed, that has elevated stem cells to iconic medical marvel, the means one day of perhaps repairing - even regenerating - tissues and organs damaged and destroyed by disease, accident and age.
CANCER
But, there's a dark side to this power of self-renewal. It's called cancer. And evidence grows daily that many - if not all - types of cancers are the consequence of normal stem cells gone bad.
"To use a Star Wars analogy, it's Jedi Knights and Darth Vader," said Dr. Evan Snyder, director of the Stem Cells and Regeneration Programme at the Burnham Institute in San Diego. "Normal stem cells have these amazing powers to differentiate into other cells, to move about the body, to go where they're needed. Cancer stem cells have the same skills, but they use them for evil."
Think of cancer as a disease of uncontrolled self-renewal, said Tannishtha Reya, an assistant professor of pharmacology and cancer biology at Duke University. Normal stem cells renew themselves under precise and carefully-regulated conditions, so their progeny are exactly what is intended and needed. Cancer stem cells do not. They simply grow amok, producing countless lesser copies that corrupt and may eventually kill.
A tumour is, in this sense, really just an aberrant organ. For decades, researchers have focused on treating cancer through reduction. If a therapy killed cancerous cells, if it reduced the size of a tumour, it was deemed a success. Clinical trials to test new cancer drugs were - and are - largely based on how well they reduce the number of detectable cancer cells or shrink tumours.
TRANSIENT VICTORIES
The tragedy, of course, is that such victories are often transient. The cancer returns, sometimes worse than before.
"There are many things that shrink tumours," said Dr. Max Wicha, director of the University of Michigan's Comprehensive Cancer Centre, "but hardly any that affect the life spans of patients."
Again, the villain may well be cancer stem cells, the small subset of cells that have the capacity to perpetuate cancer and which are resistant, if not impervious, to most common cancer drugs and treatments. Chemotherapy and radiation may kill 99 per cent of the cells in a malignant tumour, but if the remaining one per cent contain cancer stem cells, the tumour will likely grow back.
"We're talking about a fundamental paradigm change," said Wicha, whose particular interest is how breast cancer cells grow and metastasise.
"We need to develop drugs targeted at the tumour's stem cells. If we are to have any real cures in advanced breast cancer, it will be absolutely necessary to eliminate these cells. What this means for women with cancer is that, for the first time, we can define what we believe are the important cells, the cells that determine whether the cancer will come back or be cured. Before this, we didn't even know there were such cells."
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