CT Screening Overdiagnoses Lung Cancer

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A trial study conducted by the National Lung Screening Trial (NLST) showed that around 18% of lung cancers detected by low-dose CT screening were slow-growing tumors that would not have had any consequence on patients during their lifetime.

Edward F. Patz Jr., MD, of Duke University Medical Center, and co-workers discovered that the trial revealed a mortality advantage to screening, but for every one lung cancer death prevented for every 320 patients with screening in the trial, 1.38 cases of overdiagnosis would be anticipated.

"These overdiagnosis cases represent an important potential harm of screening because they incur additional cost, anxiety, and morbidity associated with cancer treatment," they wrote in the online journal, JAMA Internal Medicine.

Patz and his peers recommended that physicians make it a point to include the risk of overdiagnosis when describing the risks of low-dose CT screening for lung cancer to patients.

“While the findings may help shape patient expectations, they wouldn't likely shift the risk-benefit ratio much for individual patient. Nor is the recent U.S. Preventive Services Task Force recommendation to screen high-risk patients annually likely to be affected,” Patz explained.

"I don't think this will shift recommendations at all. It's just part of this entire puzzle we're trying to piece together, how we can best offer a mass screening program as public policy,” he added.

In response, the American College of Radiology (ACR) agreed with the study, releasing a statement calling the overdiagnosis rate "modest" and appropriate with the estimated rate with other forms of cancer screening.

“Lung cancer screening using low-dose CT is the only test ever shown to reduce mortality in high-risk smokers, the leading cause of cancer death in the U.S. It does so cost effectively compared to other screening tests. Overdiagnosis is an expected part of any screening program and does not alter these facts,”the statement read.

Preparations for the lung cancer screening programs throughout the country should go on as the medical community continues to concentrate on the issue of overdiagnosis, the ACR suggested.

The organization said it plans to move on with its efforts to support those programs, which include establishing suitable criteria and making a structured reporting and data collecting system to standardize methods.

Most programs seem to be following the NLST or altered versions of its criteria.

The trial randomized 53,454 men and women ages 55 to 74 with at least a 30 pack-year history of smoking to screening using low-dose CT or chest radiography.

During the average 6.4 years of follow-up, CT-based screening picked up 1,089 lung cancers as opposed to 969 in the chest x-ray arm.

“Since the actual cancer rate was likely the same between the two well-matched groups, those extra cancers detected could have represented overdiagnosis, “the researchers explained.CT Screening Overdiagnoses Lung Cance

The surplus cancer rates were 18.5% when deliberated as a possibility that the CT-detected cancer wouldn't have become clinically apparent during the screening period if CT wouldn't have been done and 11% when calculated more from a public health viewpoint as the portion of all lung cancer cases diagnosed in the study that wouldn't have been diagnosed then without CT screening.

The overdiagnosis rate was 31% when compared with no screening.

The likelihood that a tumor represented an overdiagnosis as opposed to a chest x-ray screening was also higher at 22.5% for non-small cell lung cancer and at 78.9% for bronchoalveolar lung cancer.

"These data raise the question as to the necessity and type of therapy required if a diagnosis of minimally invasive adenocarcinoma is established and challenge the diagnostic community to develop a classification scheme that could accurately phenotype all lung tumors," Patz's group wrote.

“The 4 to 5 years of follow-up after screening may not have been long enough to account for the lead time of all low-dose CT-detected cancers, particularly because tumor growth rates are quite variable and do not consistently follow classical expected exponential growth curves," the researchers cautioned.

“Because CT screening found smaller, earlier stage tumors than chest x-ray, that arm would likely have had additional cancer rate "catch up" over time, so the overdiagnosis estimates provide an upper bound on the true overdiagnosis rate associated with low-dose CT screening relative to chest radiology screening," they explained.

Patz ultimately recommended that the key to decreasing the danger of overdiagnosis will be to identify biomarkers to mark and single out the idle lung cancers.


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