Oslo January, 31 2013
Clarion Hotel Royal Christiania, Oslo, Norway
Less disagreement on the extent of the reduction in breast cancer mortality in mammographic screening, than the extent of overdiagnosis. This is the overall result from the presentations and discussion among a discussion between more than 200 experts in mammographic screening gathered in Oslo for the conference “Benefits and harms of mammographic screening - what are the disagreements?”
The best study design is randomized clinical trials. However, for mammographic screening, trials of this type were mostly done more than twenty years ago and are difficult to repeat. Their relevance for present day state of the art was discussed. Observational studies will thus provide the main contribution to new information ; those using individual level data are best because they directly link the women’s individual screening history to the outcome of interest. Another issue that was discussed was follow-up. This needs to be long enough to see the long term benefits and harms of screening, probably more than ten years.
The estimates on mortality reduction – for women that have been invited to screening, ranged from 10% to 30%. But for those that attend the screening program, the mortality reduction range from 38% to 48%. The estimates of overdiagnosis (defined as cancers that will not treten the life f he women during their expected lifetime) ranged from 7% to 50%. The UK independent panel reported 11% to 19%. Interestingly, recently published results from Norway based on individual-level data ranged from 10% to 20%.
An issue related to overdiagnosis is overtreatment, which needs to be minimized for all stages of breast cancer.
The risk of a false positive screening result (recall for further examination because og doubtfull mammogram resuling in a no cancer diagnosis) during ten screening examinations from age 50 is estimated to be 20%. Most of the studies show that recall related anxiety is short lived.
Communicating the uncertainties of these findings as accurately as possible to the women, so that women can make the best informed choice should be a goal.