Research
Time lag to benefit after screening for breast and colorectal cancer: meta-analysis of survival data from the United States, Sweden, United Kingdom, and Denmark
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BMJ
2013;346:e8441
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We agree that there is substantial uncertainty regarding the magnitude of harms from overdiagnosis and overtreatment for breast and colorectal cancer screening. One reason we presented a range of time-lags to benefit corresponding to different absolute risk reductions in cancer mortality (1 in 10,000 to 1 in 500) was the uncertainty regarding the magnitude of harms for cancer screening. Thus, our range of time-lags to benefit could be viewed as a sensitivity analysis.
As a meta-analysis, we were constrained by the follow-up times reported in the original studies. Rather than extrapolating our results beyond the data, we await the longer term follow-up data from the meta-analyzed studies to shed light on the mortality benefits of breast and colorectal cancer screening beyond 15 years.
Competing interests: None declared
UCSF, 4150 Clement Street, San Francisco, CA 94121
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17 January 2013
The authors' conclusion does not follow from the data presented or the argument.
The study indicates that, on average, screening makes one out of 6 deaths preventable for colorectal cancer, and one out of 4 - for breast cancer. This proportion seems to be slightly increasing with time but generally is fairly stable.
Lee et al are suggesting that screening is less appropriate for patients with a life expectancy less than 10 years on the basis that there is a chance of patients being harmed, sometimes seriously, from screening. The authors, however, do not provide any meaningful quantitative comparison between the risk of being harmed from screening and the risk of preventable death occurring due the absence of screening.
The negative values of these risks are incommensurable and are different for different patients. The only meaningful conclusion from the data presented by Lee et al is that the data and the argument support an individualized process of decision making in cancer screening in particular and medical care in general.
Competing interests: None declared
Independent, London W8
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Lee et al should have provided a sensitivity analysis with a range for overdiagnosis estimates. The USPTF reference 37 gives a low-ball estimate of 1/1000. Cochrane (ref 9) calculated the harm of overdiagnosis and overtreatment as 5/1000, 5 times higher than the what the authors used. Would the authors extend the graph?-if extrapolated, this puts the time to a net benefit at 30+ years? Therefore no woman over age 60? would benefit. The harm of false positives would also greatly increase with the longer time.
Competing interests: None declared
Stroger Cook County Hospital, 1901 West Harrison Street Chicago IL
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