One in three breast cancers 'harmless

Published on 09/07/2009 22:00

AS MANY as one in three breast cancers detected by screening may actually be harmless and not need treatment, new research has found.

The study, which analysed data from the UK, Canada, Australia, Sweden and Norway, suggests some women undergo unnecessary treatment for cancers that are unlikely to kill them or spread. But campaigners have urged women to continue to go for screening, as research showed it saved many lives every year.

In Scotland, women are invited for a mammogram to check their breasts every three years between the ages of 50 and 70. In the latest study, researchers from the Nordic Cochrane Centre in Denmark pointed out that some breast cancers could grow so slowly that the patient died of other causes first, or the cancer might stay dormant or regress.

Writing in the British Medical Journal, the scientists said cancer screening programmes could lead to "overdiagnosis" as a result.

They added: "Screening for cancer may lead to earlier detection of lethal cancers, but also detects harmless ones that will not cause death or symptoms. The detection of such cancers, which would not have been identified clinically in someone's remaining lifetime, is called overdiagnosis and can only be harmful to those who experience it.

"As it is not possible to distinguish between lethal and harmless cancers, all detected cancers are treated. Overdiagnosis and overtreatment are therefore inevitable."

The authors said autopsy data showed that about 37 per cent of women aged 40 to 54 who died from causes other than breast cancer "had lesions of invasive or non-invasive cancer".

About half these lesions would have been picked up in screening and some would have been treated, they said.

The experts focused on data between 1971 and 1999. They looked at breast cancer trends before and after the introduction of government-funded screening programmes in all the countries studied, covering at least seven years before and after screening was implemented.

The researchers found an increase in the incidence of breast cancer that was closely related to the introduction of screening programmes. They estimated the level of overdiagnosis for each country and found it to be between 46 per cent and 59 per cent, with a total overdiagnosis of 52 per cent – meaning one in three cancers was overdiagnosed. For the UK, they estimated 57 per cent overdiagnosis.

In an accompanying editorial to the research, US-based Professor H Gilbert Welch said:

"Mammography is one of medicine's 'close calls' – a delicate balance between benefits and harms – where different people in the same situation might reasonably make different choices.

"It undoubtedly helps some women, but hurts others. No right answer exists – instead, it is a personal choice."

However, campaigners urged women not to be put off screening because of the research.

Emma Pennery, of the charity Breast Cancer Care, said: "Until it is possible to accurately determine the progression of cancers found, screening remains an effective option for detecting breast cancers as soon as possible.

"Without screening, women would face the prospect of having to wait for a visible symptom of cancer, such as a lump, to become apparent before treatment could start.

"We know that early detection of breast cancer may lead to simpler, more effective outcomes and would urge women not to be put off breast screening by this report."

Dr Sarah Cant, of Breakthrough Breast Cancer, said: "We believe the benefits of detecting breast cancer early still outweigh the risks.

"Breakthrough agrees that women need to be given clear information about both the risks and benefits of breast screening so they can make informed choices. While survival rates have increased greatly in recent years, just under 12,000 women still die from this disease each year in the UK."

Dr Laura Bell, Cancer Research UK's information officer, said the screening programme in the UK prevented more than 1,000 breast cancer deaths a year, and she urged women to attend.

Health secretary Nicola Sturgeon added: "One in nine Scottish women will suffer breast cancer at some time in her life. Treatment is most successful when breast cancer is found early, so being screened is absolutely vital for women over 50.

"It is important that all abnormalities identified by screening are investigated. Even if these abnormalities are found to be less sinister than they could have been, we see this as a positive outcome for the woman concerned.

"Scotland's screening programme makes every effort to explain to women the potential benefits and risks of breast screening, so they can make informed choices."

ROUTINE SCREENING PICKED UP EARLY SIGNS

LINDA Milton was invited for breast cancer screening in 2000 after she turned 50.

The mammogram showed up areas of concern, which led to her having a biopsy.

The tests found signs of ductal carcinoma in situ (DCIS) – cells in some of the ducts of the breast had started to turn into cancer cells.

Mrs Milton, 59, from Clarkston, Glasgow, had the breast removed.

When the results came back, it showed the cancer was becoming more invasive.

"If I had let sleeping dogs lie, the dogs might have started to bite," she said.

Mrs Milton had to take the drug Tamoxifen for three years after her operation, followed by two years of Arimidex.

She said: "I am always shouting at people to go for their breast screening.

"The earlier you find it, the better the chances of doing something about it.

"I have absolutely no regrets that I went for it and it was picked up because I might not be here otherwise."