Breast screening study sparks controversy

by Gary Finnegan – World Health Matters (Sweden) –

Breast cancer screening has limited or no impact on breast cancer mortality among women aged 40-69, according to a study published in the Journal of The National Cancer Institute. The findings are based on cancer mortality data from Sweden and are consistent with some studies conducted elsewhere but the research has come in for some criticism.

While the trends revealed by the study could lead to questions over the validity of investing in mammography programmes, experts who were not involved in the study say the conclusions reached by the researchers should be read with caution given the number of additional factors which could have coloured the results but may not be accounted for in the new paper.

Since 1974, Swedish women aged 40-69 have increasingly been offered mammography screening, with nationwide coverage peaking in 1997. The researchers said their goal was to determine whether mortality trends have shifted in response to the screening programme.

Figures from the Swedish Board of Health and Welfare from 1960 to 2009 were analysed in order to compare actual mortality outcomes with the reductions seen in theoretical models.

The researchers said they expected that screening would indeed be associated with a gradual reduction in mortality. However, their study found that breast cancer mortality rates in Swedish women started to decrease in 1972, before the introduction of mammography, and have continued to decline at a rate similar to that in the pre-screening period.

“It seems paradoxical that the downward trends in breast cancer mortality in Sweden have evolved practically as if screening had never existed,” they write. “Swedish breast cancer mortality statistics are consistent with studies that show limited or no impact of screening on mortality from breast cancer.”

The researchers do note certain limitations of their study – namely, that it was observational, so unable to take into account the potential influence of other breast cancer risk factors such as obesity, which may have masked the effect of screening on mortality. They also write that population mobility may have biased the results.

However, an accompanying editorial by Dr Nereo Segnan of the Giovanni Battista University Hospital in Italy, and a separate commentary by Dr Michael W Vannier of the University of Chicago Medical Center, questioned the validity of the findings and supported the continued use of mammography screening.