The findings have intensified the debate about the ethics and safety of egg donation and whether donors should be paid.

Infertility specialists from the Cromwell Hospital, a private hospital in west London, have warned that until the extent of the risk is properly evaluated a ban should be placed on "altruistic" egg donation.

They suggest that unpaid egg donations should be replaced with volunteer egg-sharing schemes among women undergoing fertility treatment. Such a scheme operates at the hospital with women offered subsidised IVF if they agree to share remaining eggs.

However subsidised egg sharing schemes may be outlawed by the Human Fertilisation and Embryology Authority, which fears donors could blame their lack of IVF success on the fact that half of their eggs were given away.

Drug link

The Cromwell team scrutinised more than 60 studies in which hundreds of cases of cancer have been linked to drugs used to stimulate the ovaries before donation.

Their report found evidence of a link between egg donation and cancer, mainly of the breast and ovary, infertility and deep-vein thrombosis.

They are concerned that although a link may exist, many clinics are increasingly advertising for "altruistic" donors to meet a growing demand for eggs.

The report states: "Conventional non-patient egg donors undergo ovarian stimulation by treatment with fertility drugs. Egg-sharing reduces or eliminates the need for such extra stimulation, thus meeting a key requirement of the HFEA code of practice that 'centres should take all reasonable steps to ensure that people receiving treatment and any children resulting from it have the best possible protection from harm to their health'."

Growing evidence

Cromwell Hospital director Dr Kamal Ahuja said: "There is a growing body of evidence in the medical literature that suggests a link between egg donation and cancer. The link is unproven at the moment but it is rapidly becoming worrying.

"At the moment for every donor who comes forward there are 20-30 potential recipients waiting. With waiting lists for donor eggs growing rapidly, clinics are forced to advertise for donors or close."

A HFEA spokesman said: "Following concerns that there might be a possible link between taking drugs to stimulate the ovaries and the risk of ovarian cancer, experts have recognised the need to undertake further studies to establish whether there is such a link. A positive casual link has not however been sufficiently proven."