Prozac link to cancer growth

Laboratory research has shown the pill and similar anti-depressants stimulate the growth of tumours by blocking the body’s natural ability to kill cancer cells.

Support groups last night described the findings as "very worrying" but urged patients not to stop taking their medication until further studies are undertaken.

Professor John Gordon, of Birmingham University, reported that in test-tube experiments, Prozac and other widely-prescribed selective serotonin re-uptake inhibitors (SSRIs), such as Paxil and Celexa, encouraged growth of a type of cancer called Burkitt’s lymphoma.

Serotonin is a naturally occurring chemical that regulates people’s moods. Those with too little often suffer depression.

Drugs such as Prozac work by preventing serotonin from being reabsorbed too quickly by the nerve cells in the brain.

However, the study, to be published in the medical journal Blood next week, found that serotonin was a key driver in stimulating a natural cell "suicide" process for controlling the runaway growth that leads to cancer.

The anti-depressants prevented serotonin from being absorbed into the cancer cells, leading to a more vigorous growth of the tumours.

Prof Gordon, whose study was part funded by the Medical Research Council, said it was still premature to suggest the drugs were unsafe, but the Depression Alliance warned more research into the link was vital.

Prof Gordon said: "We’ve shown that, in the test-tube, the SSRIs stop the action of the serotonin on the cancer cells. But it’s impossible to extrapolate to what’s happening in the body.

"An exciting property of serotonin is that it can tell some cells to self-destruct. We have found serotonin can get inside the lymphoma cells and instruct them to commit suicide, thereby providing the potential for an effective therapy."

He and his team examined Burkitt’s lymphoma, a particularly aggressive tumour of the white blood cells that manifests itself in large tumours in the jaw and abdomen.

He said: "We were looking at what could kill these tumours and we found adding serotonin to them killed them quickly and effectively. We are hoping to use these findings to develop a drug to treat the cancer."

While there is no evidence to date from clinical trials on people to back up the concerns, the finding has triggered fresh debate about Prozac, which first went on sale in the 1980s, and its counterparts.

Last September, a major class-action lawsuit was filed in California against GlaxoSmithKline, the drug company that makes Paxil, by a group who claim to have become dependent on the drug.

Paxil, also known as Seroxat, has overtaken Prozac as the world’s best-selling SSRI with sales last year of 1.86 billion.

A spokeswoman for the Depression Alliance said: "This new research is very worrying. But a link between an increased risk of cancer and Prozac use has not yet been established. Much more research into this topic must be done.

"Depression Alliance would strongly recommend that people do not stop using their medication but seek advice from their doctor or pharmacist ."

Depression is one of the most common conditions in the UK, affecting one in five people at some stage in their life. In Scotland, more than 300,000 people are currently diagnosed as suffering from the condition, two thirds of whom are women.

Millions of people with depression, anxiety, obsessive-compulsive disorder and bulimia nervosa have been prescribed SSRIs, which have emerged as one of the biggest sellers for the international pharmaceutical industry, and doctors in Britain issue about three million prescriptions for the drugs each year.

Yesterday, drug company officials said there was no evidence that their pills caused any increase of cancer in practice and questioned whether the high doses used in Prof Gordon’s experiments may have been responsible for the results. A spokesman for GlaxoSmithKline said: "These data are from an in vitro [test tube] study and as such they cannot be extrapolated to a clinical setting with any degree of certainty."

A Department of Health spokesman said as yet no increased risk of cancer had been detected in patients.

The World Health Organisation estimates that by 2020, depression will be the biggest global health concern after chronic heart disease.