A variety of estimates of the benefits and harms of mammographic screening for breast cancer have been published and national policies vary.
The objective of a review was assess the effect of screening for breast cancer with mammography on mortality and morbidity.
Selection criteria were randomised trials comparing mammographic screening with no mammographic screening.
Eight eligible trials were identified. Researchers excluded a trial because the randomisation had failed to produce comparable groups.
The eligible trials included 600,000 women in the analyses in the age range 39 to 74 years.
Three trials with adequate randomisation did not show a statistically significant reduction in breast cancer mortality at 13 years ( relative risk, RR=0.90, 95% confidence interval (CI) 0.79 to 1.02 ); four trials with suboptimal randomisation showed a significant reduction in breast cancer mortality with an RR of 0.75 ( 95% CI 0.67 to 0.83 ).
The relative risk for all seven trials combined was 0.81 ( 95% CI 0.74 to 0.87 ).
Researches found that breast cancer mortality was an unreliable outcome that was biased in favour of screening, mainly because of differential misclassification of cause of death.
The trials with adequate randomisation did not find an effect of screening on total cancer mortality, including breast cancer, after 10 years ( RR 1.02, 95% CI 0.95 to 1.10 ) or on all-cause mortality after 13 years ( RR 0.99, 95% CI 0.95 to 1.03 ).
Total numbers of lumpectomies and mastectomies were significantly larger in the screened groups ( RR=1.31, 95% CI 1.22 to 1.42 ), as were number of mastectomies ( RR 1.20, 95% CI 1.08 to 1.32 ).
The use of radiotherapy was similarly increased whereas there was no difference in the use of chemotherapy ( data available in only two trials ).
In conclusion: if we assume that screening reduces breast cancer mortality by 15% and that overdiagnosis and overtreatment is at 30%, it means that for every 2000 women invited for screening throughout 10 years, one will avoid dying of breast cancer and 10 healthy women, who would not have been diagnosed if there had not been screening, will be treated unnecessarily.
Furthermore, more than 200 women will experience important psychological distress including anxiety and uncertainty for years because of false positive findings.
Because of substantial advances in treatment and greater breast cancer awareness since the trials were carried out, it is likely that the absolute effect of screening today is smaller than in the trials.
Recent observational studies show more overdiagnosis than in the trials and very little or no reduction in the incidence of advanced cancers with screening. ( Xagena )
Gøtzsche PC, Jørgensen KJ, Cochrane Database of Systematic Reviews 2013, Issue 6. Art. No.: CD001877. DOI: 10.1002/14651858.CD001877.pub5.