Doctors have long struggled to differentiate cancerous stem cells from healthy ones, but Canadian researchers now say they know how to tell the two apart to hopefully one day better identify how to kill only the dangerous ones.

The discovery, published Sunday in the journal Nature Biotechnology, may eventually allow further targeting of cancer treatments.

Specifically, Dr. Mick Bhatia of Hamilton's McMaster University and his team have demonstrated for the first time how to tell the difference between normal stem cells and cancer stem cells in humans.

"Normal stem cells and cancer stem cells are hard to tell apart, and many have misconstrued really good stem cells for cancer stem cells that have gone bad — we now can tell the ones masquerading as normal stem cells from the bad, cancerous ones," Dr. Bhatia, scientific director of the Stem Cell and Cancer Research Institute at McMaster University in Hamilton, Ont., said in a release. (Listen to CBC radio's Quirks and Quarks interview with Dr. Bhatia.)

"This also allows us to compare normal versus cancer stem cells from humans in the laboratory — define the differences in terms of genes they express and drugs they respond to. Essentially, we can now use this to find the 'magic bullet,' a drug or set of drugs that kill cancer stem cells first, and spare the normal healthy ones," he said.

The research also helps allay one of the big worries about one day using stem cells to grow new organs and other tissues for curing disease — that the stem cells could give rise to tumours and end up doing more harm than good.

Stem cells are master cells

Known as the body's master cells, stem cells have the ability to give rise to, or differentiate into, any tissue type — from heart, lung and liver, to brain, bone and skin. Unlike mature cells, which remain the same throughout their lifespan, stem cells can both renew themselves and create new cells of whatever tissue type they belong to.

Cancer stem cells, on the other hand, give rise to cancerous cells.

Bhatia said scientists working in labs worldwide, including his own, would assume that their particular stem cell lines were healthy and able to give rise to an array of similarly healthy cells of varying types. (A stem cell line is a family of constantly dividing cells arising from a parent group of stem cells.)

But often when researchers tried to use these so-called high-quality stem cells in experiments, they found the cells didn't behave as they had hoped.

For example, the McMaster lab manipulated human embryonic stem cells to produce brain cells and implanted them into mice. But instead of producing normal, healthy neurons, they produced a tumour.

With files from the Canadian Press