Estimated Lifetime Gained With Cancer Screening Tests
A Meta-Analysis of Randomized Clinical Trials
Michael Bretthauer, MD, PhD; Paulina Wieszczy, MSc, PhD; Magnus Løberg, MD, PhDet alMichal F. Kaminski, MD, PhD; Tarjei Fiskergård Werner, MSc; Lise M. Helsingen, MD, PhD; Yuichi Mori, MD, PhD; Øyvind Holme, MD, PhD; Hans-Olov Adami, MD, PhD; Mette Kalager, MD, PhD
JAMA Intern Med. Published online August 28, 2023. doi:10.1001/jamainternmed.2023.3798
This is a systematic review and meta-analysis published by authors from the Institute of Health and Society at the University of Oslo (Norway), examining 18 long-term randomized clinical trials, seeking to estimate the length of life 'gained' through cancer screening.
Several screening tests are analyzed: mammography screening for breast cancer; colonoscopy, sigmoidoscopy, fecal occult blood testing(FOBT) for colorectal cancer; CT screening for lung cancer in current and former smokers; prostate-specific antigen (PSA) testing for prostate cancer.
The study involves 2.1 million people, more precisely 721,718 men for PSA screening, 614,431 men and women for sigmoidoscopy screening, 598,934 men and women for fecal blood testing every two years, 84,585 men and women for colonoscopy screening and 73,634 women for mammography screening ; a smaller sample size for annual fecal blood screening (30,964 men and women) and lung cancer CT screening (20,505 men and women).
The review covers trials with more than 9 years of follow-up (10 to 15 years of follow-up on average) reporting all-cause mortality and estimated acquired life expectancy for 6 commonly used cancer screening tests, comparing 'screening' with 'no screening'.
The endpoint was the duration of life in the 'screening' groups compared with the 'non-screening' groups, based on reported data for all-cause mortality and cancer-specific mortality.
In other words, the years of life "gained" by screening were calculated as the difference in observed lifespan (in person-years) between the "screening" and "non-screening" groups.
The analysis focused on the general population.
MEDLINE and Cochrane Library databases were used as the basis for this search.
Observational and modelling studies were not included due to multiple potential biases.
Key points and main results :
Question: Cancer screening tests are promoted to save lives, but to what extent is life actually prolonged by commonly used cancer screening tests?
Answer: The results of this meta-analysis suggest that colorectal cancer screening by sigmoidoscopy can prolong life by around 3 months; the gain in life span for other screening tests seems unlikely or uncertain.
In this figure, horizontal arrows illustrate four people who underwent screening.
Arrows pointing to the right: 2 people who benefited from screening live longer thanks to early cancer detection and cure.
Arrows pointing to the left: 2 people who suffered screening-related harm and died earlier than those who were not screened.
The blue circle shows the effect of screening on population longevity, calculated as the sum of all individual benefits minus all individual harms.
We can see that, overall, there is no net gain in life expectancy, which is what screening promised when the national campaigns were launched.
The authors write: “Based on the observed relative risks for all-cause mortality and the reported follow-up time in the trials, the only screening test that significantly increased longevity was sigmoidoscopy, by 110 days (95% CI, 0-274 days) (Table 2..).
We found no statistically significant outcomes for longevity with mammography screening (0 days; 95% CI, −190 to 237 days) and FOBT screening with yearly or biennial screening (0 days; 95% CI, −70.7 to 70.7 days).
Colonoscopy screening (37 days; 95% CI, −146 to 146 days) and PSA screening (37 days; 95% CI, −37 to 73 days) may have an association with longevity of about 5 weeks, and lung cancer screening among smokers or former smokers of about 3 months (107 days; 95% CI, −286 to 430 days), but these estimates are uncertain (Table 2..)“
Right: life "gained"; left: life "lost".
Diamond dots indicate point estimates of days of life gained or lost for each screening test. Left and right arrows indicate the 95% confidence interval.
CT stands for computed tomography for lung cancer, FOBT for faecal occult blood test, and PSA for prostate-specific antigen.
The authors elaborate on their findings.
“Our study quantifies whether use of 6 commonly used cancer screening tests is associated with length of life. One test (sigmoidoscopy) significantly prolonged life and longevity by 110 days, although the lower bound of the 95% CI extended to 0. Fecal testing and mammography screening did not appear to prolong life in the trials, while estimates for prostate cancer screening and lung cancer screening are uncertain.
In recent decades, organized cancer screening programs have been established in Europe, Canada, the Pacific Islands, and in many countries in Asia. In the US, cancer screening is offered by many institutions and encouraged and reimbursed by most health care payers. Several studies have investigated the association between screening and all-cause mortality.6,28 Few have translated their results to practical and easy-to-grasp estimates for health care professionals and individuals on how much cancer screening may increase life expectancy. Our study provides these estimates."
“Even if we did not observe longer lives in general with 5 of the 6 screening tests, some individuals prolong their life due to these screening tests. Cancer is prevented or detected in an early stage, and the individuals survive screening and subsequent treatment without harms or complications. Without screening, these patients may have died of cancer because it would have been detected at a later, incurable stage. Thus, these patients experience a gain in lifetime. “
"However, other individuals experience a lifetime loss due to screening.35,36 This loss is caused by harms associated with screening or with treatment of screening-detected cancers, for example, due to colon perforation during colonoscopy or myocardial infarction following radical prostatectomy.37,38
For 5 of the 6 screening tests investigated herein, the findings suggest that most individuals will not have any gain in longevity.
For those who have their longevity altered with screening, the cumulative loss for those who are harmed must be outweighed in duration by the cumulative gain experienced by those who benefit to show unchanged lifetime in individuals who undergo screening compared with those who do not”.
“Our study may provide easy-to-understand estimates for prolongation of life attributable to screening that may be used in shared decision-making with individuals who consider undergoing a screening test. Our estimates may also serve to prioritize public health initiatives in comparison with other preventive measures, such as obesity treatment or prevention of cardiovascular disease.28
The lack of increased longevity with screening may also occur due to competing causes of death. Many of the cancers we are screening for share risk factors with more prevalent causes of death, such as cardiovascular and metabolic diseases. A lack of a significant increase in longevity due to cancer screening may therefore be due to death from competing causes at the same time a patient would have died of cancer without screening. A mortality shift from cancer to other causes of death without increased length of life is thus plausible."
“Due to the stigma and the psychological burden, a cancer diagnosis may also cause extra noncancer-specific deaths from suicide, cardiovascular disease, and accidents.41,42 Also, increased surveillance after cancer screening may increase the risk of other incidental disease, which would not have been detected without screening.43
Adherence to more than 1 screening test may potentially increase longevity. The one study that was available28 does not suggest that there is an additive effect of screening for more than 1 cancer. Although such outcomes are possible, the competing risk of other disease might also outweigh the influence of screening for 2 or more cancer sites on length of life...."
Another concern addressed by the authors is quality of life after cancer:
« In addition to lifetime gained or lost with screening, quality of life is important. Quality-adjusted life-years (QALYs) are difficult to measure and interpret, but recent analyses of QALYs for mammography screening estimates in Norway suggest that net QALY in modern mammography screening in Norway may be negative.29 »
Conclusions and relevance of the study:
The results of this meta-analysis suggest that current evidence does not support the claim that cancer screening tests save lives by extending lifespan, with the possible exception of sigmoidoscopy screening for colorectal cancer.
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