Screening for breast cancer with mammography
There have been several published estimates of the benefits and harms of mammographic screening for breast cancer. The objective of this review was to assess the effect of screening for breast cancer with mammography on mortality and morbidity. The review included seven randomised trials comparing mammographic screening with no mammorgraphic screening, with a total of 600 000 women. The pooled risk ratio from the meta-analysis of breast cancer mortality for all trials combined was 0.81 ( 95% CI 0.74 to 0.87), indicating a reduced risk. However, the authors found that breast cancer mortality was an unreliable outcome that was biased in favour of screening. The trials with adequate randomisation did not find an effect of screening on cancer mortality after 10 years or on all-cause mortality after 13 years. The review found that screening is likely to reduce breast cancer mortality, with an absolute risk reduction of 0.05%. Furthermore, screening was found to lead to 30% over-diagnosis and overtreatment, or an absolute risk increase of 0.5% of these outcomes. This means that for every 2000 women invited for screening throughout 10 years, one will have her life prolonged 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 for many months because of false positive findings. The review’s authors concluded that it is not clear whether screening does more good than harm.
Gøtzsche PC, Nielsen M. (2011) Screening for breast cancer with mammography. Cochrane Database of Systematic Reviews, Issue 1.
Screening for prostate cancer
The review’s objective was to update a previous review and determine whether screening for prostate cancer reduces prostate cancer-specific mortality and all-cause mortality; and assess its impact on quality of life, including adverse events. Five RCTs with a total of 341,351 participants were included in this review, with three studies being assessed as posing a high risk of bias. The meta-analysis of the five studies indicated no statistically significant reduction in prostate cancer-specific or all-cause mortality among the whole population of men randomised to screening compared controls. The probability of receiving a diagnosis of prostate cancer was significantly greater in men randomised to screening, compared to those randomised to control (relative risk 1.35, 95% CI 1.06 to 1.72). The studies did not provide any detailed assessments of the effect of screening on quality of life or costs associated with screening. Harms of screening included high rates of false-positive results for the PSA test (up to 75.9%), over-diagnosis (up to 50% in the largest study included in the review) and adverse events associated with transrectal ultrasound guided biopsies such as infection, bleeding and pain. Only one study reported a benefit in a subgroup of men aged 55 to 69: within this subgroup it was determined that 1410 men needed to be invited to screening and 48 additional men subsequently diagnosed with prostate cancer needed to receive early intervention to prevent one additional prostate cancer death at 10 years. The review’s authors concluded that men should be informed of both the potential benefits and the demonstrated adverse effects when deciding whether or not to undergo screening for prostate cancer. Any benefits from prostate cancer screening may take up to 10 years to accrue; therefore, men who have a life expectancy less than 10 to 15 years should be informed that screening for prostate cancer is unlikely to be beneficial.
Ilic D, et al. (2006) Screening for prostate cancer. Cochrane Database of Systematic Review, Issue 3.