Tumour evidence may force rethink on Prozac

By STEVE CONNOR in London

Scientists have discovered that the antidepressant Prozac, taken by millions of people around the world, may stimulate the growth of brain tumours by blocking the body's natural ability to kill cancer cells.

An international team of researchers led by John Gordon, professor of immunology at Birmingham University, found evidence to suggest cancer cells can be killed by "positive thinking", which could be blocked when people take Prozac.

The study, to be published in the journal Blood, examined the effects of Prozac and other antidepressants on a group of tumour cells growing in a test tube. The researchers found that the drug prevented the cancer cells from committing "suicide", thereby leading to a more vigorous growth of the tumours.

Although an increased risk of cancer has not so far been detected in Prozac patients, the findings could lead to a re-evaluation of the drug's long-term safety.

Prozac is used for the treatment of depression, obsessive-compulsive disorder and bulimia nervosa. Doctors in Britain issue about three million prescriptions for it yearly.

Gordon said his results could not be taken as proof that Prozac stimulates tumour growth.

"Although that extrapolation could be valid, there is no direct evidence from large-scale epidemiological studies currently to back it up. However, it's important that we look again and again."

The research work was designed to find new ways of treating lymphomas by investigating how the brain communicates with the immune system to induce "positive thinking" through a neuro-transmitter in the brain called serotonin, a natural chemical that regulates people's moods.

Prozac, and other members of the class of antidepressants known as selective serotonin re-uptake inhibitors (SSRIs), works by preventing serotonin from being quickly reabsorbed by nerve cells in the brain.

The scientists tested other SSRIs and found they, too, had the same effect in stimulating the growth of a type of tumour known as Burkitt's lymphoma.

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

The researchers found Prozac blocked the entry of serotonin into the test-tube tumour cells, therefore stopping them from committing suicide.

Gordon said it was premature to suggest that the drug was unsafe.

A spokeswoman for Eli Lilly, the manufacturer of Prozac, said the research was too new for it to make a detailed response.

- INDEPENDENT

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