It is now a decade since human embryonic stem cells were discovered, and since the UK legislated to facilitate cloning human embryos for research. Since then, barely a week has passed without new stem cell stories appearing. Last November, it was widely reported that the world's "first tailor-made replacement organ", a successfully transplanted trachea produced from stem cells, finally proved the enormous potential of embryonic stem cells. The Guardian trumpeted this as "a tribute in particular to the UK regulatory framework that enabled stem cell research to make such rapid strides", concluding that "the election of Barack Obama, committed to removing the block on federal funding for most stem cell research in the US, can only speed the process." So is this, as many end-of-year commentaries implied, game, set and match to the embryo research lobby, and defeat for those advocating stem cell science that does not involve destroying human embryos?

A moment's examination shows precisely the opposite. The truth is that the airway transplant was achieved with exclusively adult stem cells, while the Obama and UK regulation references relate exclusively to embryonic stem cells. Such conflation of unrelated stem cell developments - citing adult stem cell advances to promote embryonic stem cell research - is not rare. Gordon Brown, trying to persuade MPs to support animal-human hybrid embryo research, wrote: "With adult stem cells already being used as treatments for conditions including leukaemia, severe combined immunodeficiency, and heart disease, scientists are already close to the breakthroughs that will allow embryonic stem cells to be used to treat a much wider range of conditions."

In fact, as the advantages of other forms of stem-cell research become increasingly obvious, there is every reason to predict that the use of human embryos as a source of stem cells will decline substantially this year.

It is little realised but invariably true that every media stem cell story involving patients concerns adult cells; and every story about embryonic stem cells is about their potential, or animal experiments - not patients. Embryonic stem cells remain far too dangerous for clinical testing. Cross-infection and rejection are potential problems, but the biggest hazard is that embryonic stem cells form tumours. Biologically, they have much in common with cancer stem cells.