International Federation of Gynecology and Obstetrics

Screening remains the most effective tool for discovering breast cancers as soon as possible, it has been claimed.

Dr Emma Pennery, clinical director at Breast Cancer Care, was commenting on a new study from the Nordic Cochrane Centre, Denmark, published in the British Medical Journal, which indicated that one in three breast cancers found by mammogram screening is overdiagnosed.

She accepted that treatment for breast cancer is "quite difficult" and it can be hard for people to accept if they had treatment for a cancer which was unlikely to harm them.

However, Dr Pennery added: "What is important to say is that you can't tell which of these women [treatment] would be unnecessary for and which it wouldn't.

"You can't tell what group you're in, so women will have no way of knowing whether the cancer has been overdiagnosed or whether it would have come about anyway. That's the difficulty really."

According to the UK Office for National Statistics, breast cancer is the most common cancer in England, with 38,200 new cases diagnosed in women during 2005 alone.