Scientists at McMaster University have found a way to tell the difference between normal stem cells and cancer stem cells, a discovery that removes one of the hurdles to the long-awaited promise of using human embryonic stem cells for personalized organ and tissue transplantation.

The study, published yesterday, sets out a list of criteria that scientists can use to differentiate between normal stem cells and cancer stem cells, a subset of rogue cancer cells that many scientists believe drive the growth of malignant tumours. The finding will also help in the search for new, more targeted cancer drugs.

Many of the properties of a healthy human stem cell are also the same properties of a cancer stem cell — both grow quickly, have the ability to self-renew and make copies of themselves, and they often express the same genetic markers, said Mick Bhatia, the study’s lead author and scientific director of the McMaster Stem Cell and Cancer Research Institute at the Michael G. DeGroote School of Medicine.

“What we demonstrate is that there is, in fact, a very grey line between a great stem cell and a cell that tips over into becoming a cancer stem cell,” he said.

There are lines of human embryonic stem cells in labs right now that, before this test, would be considered healthy stem cells, said Bhatia. But the test shows, in fact, that many of them are cancer stem cells.