Screening May Over-diagnose 1 In 10 Breast Cancers

Although it is widely agreed that breast screening can reduce deaths, more discussion around this negative side effect of screening is needed, say the authors.

Researchers analysed the rate of over-diagnosis of breast cancer using data from a large breast screening trial conducted in Sweden between 1976 and 1986. Over-diagnosis is defined as cases that would never have come to clinical attention without screening.

They followed trial participants until December 2001, 15 years after the trial ended using national registries to track survival and detection of breast cancer.

Fifteen years after the end of the trial, the rate of over-diagnosis of breast cancer was 10% in women randomised to screening at age 55-69 years compared with an unscreened control group.

Although earlier studies on over-diagnosis have shown rates of up to 54%, a recent study suggests a much lower rate of 1%. But none of these studies were based on direct observations, like the present one, say the authors.

"It is widely agreed that screening using mammography can reduce mortality in breast cancer. The rate of over-diagnosis is another issue to be considered in the ongoing discussion about clinical and public health implications of breast cancer screening," they conclude.

An editorial in this week's BMJ discusses the UK breast screening programme and concludes that, although breast screening by mammography is far from perfect, it does save lives.