Study: No evidence yet that screening has cut breast cancer deaths

The researchers analysed mortality trends before and after the introduction of the NHS Breast Screening Programme in 1988, using data for the whole of England (1971-2009) and statistics for the Oxford region (1979-2009). Unlike the rest of England, all causes of death, and not just the underlying cause, were available before screening was introduced in the Oxford region.

The researchers were looking for evidence of a fall in population-based breast cancer deaths that could be attributed to the implementation of breast screening.

In the Oxford region, death rates for all ages combined peaked for both underlying causes and mentions in 1985 and then started to fall, before 1988.

For deaths where breast cancer was measured as the underlying cause between 1979 and 2009, rates declined by 2.1% (95% CI -2.7 to 1.4) a year for women aged 40–49 (unscreened), and by the same percentage a year for 50–64 year olds (screened).

In England, the first estimated changes in trend occurred before screening was introduced, or before screening was likely to have had an effect (between 1982 and 1989). Thereafter, the fall was greatest in women aged under 40: 2.0% a year in 1988–2001 and by 5.0% a year in 2001–9.

But there was no evidence that declines in mortality rates were consistently greater in women in age groups and cohorts that had been screened at all, or screened several times, than in other (unscreened) women over the same time periods.

The new research contradicts the findings of an independent review commissioned by the Department of Health, and published last year.

This concluded that there was a 20% relative reduction in mortality from breast cancer in women invited for screening. The review also found that for each breast cancer death prevented, about three “overdiagnosed” cases will be identified and treated.

Lead researcher, Ms Toqir Mukhtar, says that while the new results do not rule out a benefit of breast cancer screening at the level of the individual, “the effects are not large enough to be detected at the population level.” A further analysis based on all certified causes of death did not change the results.

Ms Mukhtar describes the evaluation of the effectiveness of breast screening programmes as problematic, saying that the effect of screening on death rates needs to be considered in light of improvements in treatment, and technological advancements made in breast screening over the past 20 years.

She concludes: “Measuring the effectiveness of mammography screening is a fundamental area of concern in countries which have established mammography screening programmes.

Clinical trials have indicated that several years have to elapse between the start of screening and the emergence of a reduction in mortality. Yet our data shows that there is no evidence of an effect of mammographic screening on breast cancer mortality at the population level over an observation period of almost 40 years.”

Responding to the findings, Professor Julietta Patnick CBE, Director of the NHS Cancer Screening Programmes, said that breast screening gave “women the best chance of successful treatment.”

She added that the recent independent review, “which evaluated the evidence for the benefits and harms of breast screening in an open and transparent way…concluded that the programme saves around 1,300 lives each year in the UK.”

Professor Sir Michael Marmot, who led the independent review, said that the two major influences on breast cancer mortality trends were changes in incidence and improvements in treatment.

“Against this background, it is difficult to estimate the effects of screening on breast cancer mortality from observational data such as these. In addition, comparing trends in mortality data, for example before and after the introduction of screening, or across different age groups or socioeconomic settings, is difficult due to inherent differences between these groups.”

That is why the review relied on trial data for the best estimate of the benefits of screening, rather than observational data, he explained.

“After reviewing the available evidence, we concluded that the NHS breast screening programme confers significant benefit to women and should continue,” he said.

Source OnMedica