Women who attend the NHS breast screening programme have a higher risk of breast cancer than women who decline to participate, finds a study in this week's BMJ. This "self selection" for screening has important implications for NHS breast cancer detection targets.
Researchers at the University of Manchester investigated over 40,000 women who were invited to participate in the regional NHS breast screening programme between 1989 and 1990. Overall, 82% attended on at least one occasion and 18% never attended.
The number of non-attenders diagnosed with breast cancer was significantly less than expected, suggesting that their risk of breast cancer is lower than that in the population targeted for screening. Therefore, the risk in those who attend must be higher, say the authors. This might occur, for example, if women with a family history of breast cancer were more likely to attend.
These findings suggest that the proportion of breast cancers potentially detectable by screening is higher than expected when cancer targets were set. This may partially explain the apparent paradox that high interval cancer rates have been reported in the NHS breast screening programme despite many screening centres achieving their detection targets, say the authors. These targets now need to be revisited, they conclude.
Ciaran Woodman, Professor of Cancer Epidemiology and Public Health, University of Manchester, Withington, Manchester, UK
Risk of breast cancer in women who attend the NHS breast screening programme: cohort study BMJ Volume 323, p 140