CT lung screening of low-risk women leads to overdiagnosis

By Amerigo Allegretto, AuntMinnie.com staff writer

January 18, 2022 -- A new study from Taiwan found that performing CT lung cancer screening on mostly low-risk women who didn't smoke leads to "considerable" lung cancer overdiagnosis. The results were published January 18 in JAMA Internal Medicine.

The researchers examined the results of a low-dose CT lung screening program that included 12 million women, many of whom were at low risk of lung cancer. They found that while there was a sixfold increase in the number of early-stage cancers that were detected, there was no concomitant decline in late-stage cancers. This indicated that the program was probably detecting many cancers that never would have presented a health problem.

"Until randomized trials demonstrate value to lower-risk groups, our findings suggest that low-dose CT screening should be offered only to heavy smokers, and only following a balanced presentation of benefits and harms," wrote a team led by Wayne Gao, PhD, from Taipei Medical University in Taiwan

While CT lung cancer screening is recommended for high-risk individuals in the U.S. and other countries, opportunistic screening has become popular in Asian countries such as China, Japan, South Korea, and Taiwan. In Taiwan, smoking is not a common habit among women, with a prevalence of less than 5% since 1980.

The study authors said young women are often featured in "dramatic" promotional materials for low-dose CT lung screening programs. While Taiwanese hospitals and physicians cannot directly advertise medical services to patients, researchers said such screening has been promoted in the media and on hospital websites.

Therefore, Gao et al wanted to look at the link between opportunistic lung screening and the unintended consequence of overdiagnosis.

Out of the 12 million women screened between 2004 and 2018, 57,898 women were diagnosed with lung cancer. Rates of early-stage lung cancer increased from 2.3 cases to 14.4 cases per 100,000 from 2004 to 2018.

However, the researchers also found no significant changes in incidence of late-stage lung cancer, which increased from 18.7 to 19.3 per 100,000 after low-dose CT was introduced.

"Because the additional 12.1 per 100,000 early-stage cancers were not accompanied by a concomitant decline in late-stage cancers, virtually all the additional cancers detected represent overdiagnosis," they added.

The team also found that the five-year lung cancer survival rate more than doubled from 2004 to 2013 despite stable mortality, with a reported increase from 18% to 40%. Gao and colleagues said this is "arguably" the highest lung cancer survival rate in the world.

The researchers called for Taiwan's National Health Insurance (NHI) to continue not providing reimbursement for population-wide low-dose CT lung cancer screening. However, the authors acknowledge that their results show the financial incentives of opportunistic screening.

"Screening can be offered at reduced cost, even free, and generate downstream procedures that are reimbursed by the NHI," they said.

The study illustrates the challenges of designing a CT lung screening program that detects cancer in those most likely to be at risk, while keeping costs and rates of overdiagnosis manageable. In the U.S., lung screening guidelines were loosened in 2021 to encompass more at-risk individuals, but even the new guidelines still require individuals to have a 20 pack-year history of smoking.

Gao and colleagues cautioned that countries may face pressure to further expand lung screening to lower-risk groups, since the proportion of lung cancers in nonsmokers will rise as smoking declines. They also said that although screening is heralded for leading to increased survival, such statistics are biased by overdiagnosis.

"Sadly, judgments about the efficacy of screening based solely on detection and survival rates are a recipe for overdiagnosis," they wrote.

Dr. Ella Kazerooni from the University of Michigan told AuntMinnie.com that the study’s results would not be applicable to U.S. citizens because the individuals would not qualify for screening based on U.S. Preventive Services Task Force criteria and risk factors.

"Just because you can screen for lung cancer with a test that is safe and easy to perform doesn’t mean you should offer it without attention to a favorable balance of benefit versus harm," said Kazerooni, who is also chair of the American Cancer Society's National Lung Cancer Roundtable.

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