Scientists say that their recent review of clinical trials involving more than 2.1m people who had six kinds of common tests for cancer found screenings don’t ultimately give someone extra time beyond their regular lifespan.
But, the experts say, this doesn’t mean you should cancel your colonoscopy or mammogram appointment.
For nearly a century, doctors have been encouraging people to get routine cancer screenings: depending on age, the American Cancer Society recommends regular screenings for breast, cervical and colorectal cancer, and suggests people discuss screening for lung and prostate cancer with a doctor, particularly for those at a higher risk of the disease.
The strategy is to catch cancer early enough, even before symptoms show, so steps can be taken to improve a person’s chance of surviving their cancer and prevent premature death.
Early diagnosis has been shown to improve cancer outcomes, which is why the American Cancer Society and the WHO say routine screening is an important public health strategy, reports CNN.
Overall, cancer mortality worldwide has decreased significantly, falling 33% since 1991, partly due to early detection as well as advances in treatment and declines in smoking.
The latest study, published in JAMA Internal Medicine, found that of the six most common cancer screenings, only colorectal cancer screening with sigmoidoscopy – where doctors check the lower part of the colon or large intestine for cancer – seemed to make a difference in extending someone’s life.
It may extend life by a little more than three months, the research says.
The study team looked at clinical trials involving at least nine years of follow-up reporting and found no significant difference in lifetime gain with the other most common cancer screening tests: mammography for breast cancer, colonoscopy, faecal occult blood testing or endoscopy (FOBT), prostate-specific antigen tests, and computed tomography for current or former smokers.
“We do not advocate that all screening should be abandoned,” the researchers wrote. “Screening tests with a positive-benefit-harm balance measured in incidence and mortality of the target cancer compared with harms and burden may well be worthwhile.”
The authors say rather than emphasise that screenings save lives, doctors should be clearer about their absolute benefits, harms and burdens.
In a related publication in JAMA Internal Medicine, Dr Gilbert Welch and Dr Tanujit Dey of the Centre for Surgery and Public Health at the Department of Surgery at Brigham and Women’s Hospital wrote that with the “growing enthusiasm” for expensive multi-cancer detection blood tests, particularly among policymakers, it will be important to do large randomised clinical trials like those in this study to truly understand whether such tests save lives and warrant their costs.
Doctors are well aware that while there are significant advantages to cancer screenings, there are also some downsides.
Some positive screening results are false positives, which can lead to unnecessary anxiety as well as additional screening that can be expensive. Tests can also give a false negative, and thus a false sense of security.
Sometimes too, treatment can be unnecessary, resulting in a net harm rather than a net benefit.
“The critical question is whether the benefits for the few are sufficiently large to warrant the associated harms for many. It is entirely possible multi-cancer detection blood tests do save lives and warrant the attendant costs and harms. But we will never know unless we ask,” the authors wrote.
Dr William Dahut, chief scientific officer for the American Cancer Society, said fully determining whether cancer screenings extended life would require an extremely large clinical trial that would have to follow patients for a very long time. The trials in the newest study weren’t big enough to look at all-cause mortality, he said.
Dahut, who wasn’t involved with the new research, said if breast cancer caused 3% of all female deaths and screenings reduced these deaths by 35%, that was a good result on its own. But screenings may change mortality overall by only about 1%, which sounds less impressive but is still an improvement.
While clinical trials may not pick up on it, cancer screenings seem to have had an effect on cancer deaths, he added. Deaths cervical cancer and prostate cancer had declined over time after doctors started encouraging people to have routine tests.
“Even outside a randomised trial, you do see evidence of an impact of cancer screening,” he said.
“Screening was never designed to increase longevity. It was really designed to decrease premature deaths from cancer.
“Preventing cancer-related symptoms and premature mortality is a meaningful thing.”
Study details
Estimated Lifetime Gained With Cancer Screening Tests: A Meta-Analysis of Randomised Clinical Trials
Michael Bretthauer, Paulina Wieszczy, Magnus Løberg, et al.
Published in JAMA Internal Medicine on 28 August 2023
Abstract
Importance
Cancer screening tests are promoted to save life by increasing longevity, but it is unknown whether people will live longer with commonly used cancer screening tests.
Objective
To estimate lifetime gained with cancer screening.
Data Sources
A systematic review and meta-analysis was conducted of randomized clinical trials with more than 9 years of follow-up reporting all-cause mortality and estimated lifetime gained for 6 commonly used cancer screening tests, comparing screening with no screening. The analysis included the general population. MEDLINE and the Cochrane library databases were searched, and the last search was performed October 12, 2022.
Study Selection
Mammography screening for breast cancer; colonoscopy, sigmoidoscopy, or fecal occult blood testing (FOBT) for colorectal cancer; computed tomography screening for lung cancer in smokers and former smokers; or prostate-specific antigen testing for prostate cancer.
Data Extraction and Synthesis
Searches and selection criteria followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) reporting guideline. Data were independently extracted by a single observer, and pooled analysis of clinical trials was used for analyses.
Main Outcomes and Measures
Life-years gained by screening was calculated as the difference in observed lifetime in the screening vs the no screening groups and computed absolute lifetime gained in days with 95% CIs for each screening test from meta-analyses or single randomised clinical trials.
Results
In total, 2 111 958 individuals enrolled in randomised clinical trials comparing screening with no screening using 6 different tests were eligible. Median follow-up was 10 years for computed tomography, prostate-specific antigen testing, and colonoscopy; 13 years for mammography; and 15 years for sigmoidoscopy and FOBT. The only screening test with a significant lifetime gain was sigmoidoscopy (110 days; 95% CI, 0-274 days). There was no significant difference following mammography (0 days: 95% CI, −190 to 237 days), prostate cancer screening (37 days; 95% CI, −37 to 73 days), colonoscopy (37 days; 95% CI, −146 to 146 days), FOBT screening every year or every other year (0 days; 95% CI, −70.7 to 70.7 days), and lung cancer screening (107 days; 95% CI, −286 days to 430 days).
Conclusions and Relevance
The findings of this meta-analysis suggest that current evidence does not substantiate the claim that common cancer screening tests save lives by extending lifetime, except possibly for colorectal cancer screening with sigmoidoscopy.
See more from MedicalBrief archives:
Updated US guidelines for colorectal cancer screenings
SA team devises cost-effective genetic breast and ovarian cancer screening
Colonoscopy may not be gold standard of colon cancer screening – large randomised trial
Cancer screening – the good, the bad and the ugly