All but One Common Cancer Screening May Not Extend Lives: Study

(Rabizo Anatolii/Shutterstock)

Cancer screenings have been viewed as a life-saving early detection and prevention strategy against the disease.

However, findings published in a new meta-analysis examining more than 2.1 million people suggest that early testing may not always deliver increases in life expectancy, leading scientists to question the value of these screenings.

Sigmoidoscopy Leads in Life Expectancy

After comparing six tests commonly used to detect breast, lung, prostate, and colon cancer, only sigmoidoscopy—a medical procedure used to look for abnormalities inside the colon—showed a significant impact on life gains of 110 days.

The study, published on Aug. 28 in the Journal of the American Medical Association (JAMA) Internal Medicine, pooled results from 18 randomized clinical trials and included more than nine years of follow-up data.

There was no significant difference following mammographies, colonoscopies, fecal blood occult testing, computed tomography (CT scans), and prostate-specific antigen (PSA) testing compared to patients who had none of these screenings.

"While fecal testing and mammography screening did not prolong life ... an extension of 37 days was noted for prostate cancer screening with prostate-specific antigen testing and 107 days with lung cancer screening using computed tomography, but estimates are uncertain," the study authors wrote.

Graph showing the days of life expectancy gained versus lost across six cancer screenings. (Courtesy of JAMA)

Risks Versus Benefits

Some individuals do live longer as a result of screenings. The earlier the detection, the better the outcome regarding survival and successful treatments following diagnosis without harm or complications, the study authors wrote.

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At the same time, other individuals aren't as fortunate, with some living for a shorter time because of the dangers associated with screenings. A colonoscopy can tear the colon, and invasive prostatectomies can induce heart attacks, according to the authors.

Graph showing the benefits versus harms of cancer screenings in years gained. (Courtesy of JAMA)

While these results may suggest that claims that cancer screenings save lives are unsubstantiated, the authors don't advocate against them in the paper. Tests in which the benefits outweigh the risks may be worth it. At the same time, patients must know that their doctors will disclose potential harms without bias. This requires that medical professionals offer full transparency about tackling the disease and be willing to consider alternatives.

A 2022 study that reviewed 33 cancer screening guidelines found that several fell short of capturing the potential harms of cancer screening. The authors' conclusions echoed those of the meta-analysis, suggesting that cancer screenings should be recommended only when the benefits outweigh the risks.

The authors also pointed out that they aren't advocating against screenings but instead are trying to raise awareness so that patients and practitioners can have well-informed discussions.

“If there's overwhelming evidence of a net benefit of a screening test, we don't want to scare somebody off [from getting screened],” study author Paul Doria-Rose, chief of the National Cancer Institute's (NCI) Healthcare Assessment Research Branch, said in a statement. “But by the same token, if there's a risk that [a serious harm] could happen if you have a screening test or a follow-up diagnostic test, then it's a physician's obligation to inform patients about what the risks of those procedures are.”

Risks of Screenings

The NCI lists several possible harms associated with screenings, which include:

• Bruising, discomfort, or colon perforation when undergoing colonoscopy or sigmoidoscopy.
• Radiation exposure that can damage healthy cells.
• False-negative results, which could lead people to skip follow-up appointments despite ongoing symptoms.
• False positives resulting in anxiety and additional unnecessary testing.
• Psychological harm, such as excessive stress about preparing for the screening, waiting for results, and worrying about follow-up tests.
• Overdiagnosis of small, slow-growing cancers that would never cause any symptoms.

Benefits of Screenings

In a 2020 study published in Radiology Imaging Cancer that involved more than two decades of evidence, researchers concluded that CT scan screenings can prevent a substantial number of lung cancer-related deaths with low clinical risk.

Findings published in Cancer in 2019 (pdf) show that mammograms saved between 27,083 and 45,726 lives from breast cancer in 2018.

A 2015 study published in Digestive Diseases and Sciences claimed that randomized controlled trials of sigmoidoscopy have reduced colon cancer deaths, with some observational studies of screenings suggesting a more than 50 percent reduction in mortality.

PSA tests are simple, widely available blood tests that may help patients detect prostate cancer early. As with most cancers, prostate cancer is more likely to be cured if it's diagnosed in the early stages. However, different from the approach to many other cancers, active monitoring is often suggested before active treatment for prostate cancer, especially when the cancer is localized.

Cancer Statistics

The American Cancer Society (pdf) estimates that roughly 2 million people will be diagnosed with cancer in the United States in 2023. Approximately 297,790 women and 2,800 men will be diagnosed with breast cancer, making breast cancer the most common cancer diagnosis. Prostate cancer is the leading cancer among men and the second most commonly diagnosed overall, with 288,300 expected cases.

Rounding out the top 12 most prevalent cancers and accounting for more than three-quarters of all new cancer cases are:

• Lung cancer.
• Colorectal cancer.
• Skin melanoma.
• Bladder cancer.
• Kidney and renal pelvic cancer.
• Non-Hodgkin lymphoma.
• Uterine cancer.
• Pancreatic cancer.
• Leukemia.
• Thyroid cancer.