Stem cells from adults may cause cancer

Stem cells, often lauded as future cures for numerous diseases, are immature "master" cells that can be programmed to become many kinds of tissue, but experts have known for a long time that stem cells harvested from embryos can turn cancerous and have been linked to leukaemias and breast cancer.

Two research teams have now found that stem cells from adults can also turn into cancer, which until now was not known. It has been widely assumed that adult stem cells, taken from bone marrow for example, do not form cancers.

A Spanish team at the Universidad Autónoma de Madrid, looked at human stem cells that had been extracted from fat tissue. The stem cells were grown for up to eight months and underwent between 90 and 140 divisions to multiply in number during this time. The researchers found that when they were transplanted into animals, the oldest stem cells formed cancers.

Danish researchers from the Institute of Cancer Biology suggest the reason these stem cells become cancerous is connected to them being replicated too many times. The Danish team found that cells that became cancerous started to make an enzyme, called telomerase, which enables them to continue dividing long after they would normally stop.

The researchers in Spain say this risk is at this stage only a theory, because the stem cells treatments currently being tested in humans uses cells that are only briefly grown outside the body, however, treatments often require vast numbers of stem cells that have to be grown from very small numbers. They suggest that stem cells stored for years in banks might not be safe to use.

Antonio Bernad and colleagues suggest that the cut-off point should be around 60 divisions or generations and recommend more research be done.

Professor Christopher Higgins, of the Medical Research Council Clinical Science Centre (MRC), says that stem cell lines maintained and developed in stem cell banks over a long period of time are currently only used for research purposes and are not transplanted into people.

Higgins says they are potentially of enormous benefit for clinical treatment but as with the development of all drugs and therapies, there are safety issues that need to be investigated and resolved and the MRC is conducting extensive research to help understand the risks involved with stem cell development and to develop safe and effective therapies.

Dr Kat Arney from Cancer Research UK says research such as this is extremely important to help build up a full picture and develop the best possible treatments.

The report is published in the latest edition of the journal Cancer Research.