Foetal stem cells cause tumours: Irrelevant and obvious

Friday, 20 February, 2009

Too many people overreacting about a recently released story of a boy developing tumours subsequent to being treated by foetal stem cells, grasping onto the case as evidence for the soundness of their moral viewpoint on embryonic stem cells. A typical example is Josephine Quintavalle of Comment on Reproductive Ethics, who is reported to have said:

The risks of tumour formation in association with embryonic stem cells are widely acknowledged and one reason why there are very serious concerns about the proposed use of such cells in treating spinal cord injury in the US. It would appear from this report that foetal stem cells are similarly unstable. These are not areas of therapy we should be rushing into, whatever the ethical debates surrounding the use of embryo or foetal tissue per se.

Notice she just assumed foetal stem cells are the same as embryonic stem cells?

The first objection to this madness is simply that embryos are not foetuses and foetuses are not embryos. The paper in which this case was presented, in the journal PLoS Medicine, clearly states that the “neural stem cells used were derived from fetuses aborted at week 8-12”, and in fact defines the term fetus as “unborn offspring from the end of the 8th week after conception”.  These are not pluripotent embryonic stem cells, sourced from embryos and able to develop into many tissues. The cells used were ‘merely’ multipotent foetal neural stem cells, sourced from foetuses and only able to develop into neural tissues.

Pro-life groups, who rely on misusing words to equivocate babies with single-celled zygotes, are likely to continue making this mistake. Strangest of all, they should not be opposed to foetal stem cells, as they are sourced from abortions that would have happened anyway. In this sense, they are similar to the embryonic stem cells sourced from otherwise discarded leftover IVF embryos. Better they be used as a cure rather than be binned and incinerated, right? So, this case, while unfortunate, is irrelevant to whether embryonic stem cells should be used.

Secondly, cancer is a risk present with all stem cells (and indeed all cells). After all, stem cells are, by definition, able to proliferate – to grow and mitotically divide – many times. As a consequence, it only takes a single mutation to some aspect of growth regulation for a stem cell to become a tumour. For a normal cell to become cancerous, it must gain the ability to proliferate in addition to a lack of regulation. This has been known for ages, and is reviewed well by Michael Clarke and Michael Becker in Scientific American and, more technically, by Michael Clarke and Margeret Fuller in the journal Cell. All stem cells pose a risk of turning cancerous, regardless of whether they are adult stem cells, embryonic stem cells, or a somatic cell induced into pluripotency.

Embryonic stem cells, foetal stem cells and induced pluripotent stem cells carry such high risk of cancer for the same reason that makes them have such great potential for repairing tissue and curing disease. While adult stem cells can divide many times, only embryonic stem cells (or similar) can divide almost indefinitely.The restricted lifespan of adult stem cells make them less likely to form a tumour, but also means they have less time to repair the tissue. Preferring stem cells for this reason is rather like preferring to hire elderly people to be spies because they likely to retire or die before they go rogue or are turned into being a double agent.

Unfortunately, all current stem cell therapies with the promise of embryonic stem cells also carry the elevated risk of cancer.  So this case of a boy developing tumours from stem cell therapy, while unfortunate, was obviously going to happen to someone.


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