Screening and Lung Cancer Overdiagnosis

Lung cancer overdiagnosis from low dose CT scans estimated

(RxWiki News) Lung cancer kills more Americans than colon, breast and prostate cancers combined. And yet there’s no fool-proof way to screen for this disease. Even the most trusted tool sometimes overshoots its mark.

After analyzing data from a landmark trial, researchers have concluded that nearly 20 percent of lung cancers detected by low-dose CT (computed tomography) scans may never have caused patients a problem.

These overdiagnosed cancers, according to the researchers, led to unnecessary testing, treatment, costs, patient anxiety and additional illness for a cancer that would never have become life-threatening if left undetected.

"If you’re a smoker, talk to your doctor about lung cancer screening."

Edward F. Patz, Jr., MD, a professor of radiology and pharmacology and cancer biology at Duke University School of Medicine, and colleagues examined data from the National Lung Cancer Screening Trial (NLST).

During this trial, 53,452 people who had smoked the equivalent of a pack of cigarettes a day for 15 years (15 pack-years) were screened for lung cancer using low-dose computed tomography (LDCT).

“Low-dose computed tomography (LDCT) has been suggested as a screening tool for lung cancer, and recent results from the National Lung Cancer Screening Trial (NLST) demonstrated an encouraging 20 percent relative reduction in lung cancer-specific mortality compared with screening using chest radiography,” these researchers wrote.

Dr. Patz explained in a statement, “The NLST provided encouraging data demonstrating that lung cancer screening with CT reduces death from the disease. However, there are inherent risks with any mass screening program, and this paper investigates the probability of overdiagnosis—meaning, if some patients never would have been screened for lung cancer, they would never have known they had the disease because it would never have caused symptoms."

Using various statistical analysis methods, Dr. Patz and team looked at the NLST data from two perspectives: 1) the probability that the participants’ LDCT-screened lung cancer was slow-growing and would never have caused symptoms, and 2) the number of LDCT-detected lung cancers diagnosed that would not have been diagnosed without LDCT screening.

DailyRx News spoke with leading lung cancer expert D. Ross Camidge, MD, PhD, the director of the lung cancer clinical program at the University of Colorado Hospital in Aurora.

“To make sense of this, you have to say a perfect screening program would only catch clinically significant cancers and would catch them earlier in their course of disease, so you can intervene and change the outcome,” Dr. Camidge said.

He added that eventually the number of cancers diagnosed would be the same among screened and unscreened patients. “The stage of the cancer at the time of diagnosis and consequently the death rate from the cancers is what will differ between the two groups,” Dr. Camidge said.

He continued, “However, if you are also catching cancers that are clinically trivial, ones that would never progress to advanced stage disease and/or otherwise present clinically, then one of the imperfections in a screening program will be that there will also be a total excess of cancers in the screened arm.”

Dr. Patz’s team estimated that of all 1,089 lung cancers detected in the NLST, there was an 18.5 percent chance that it was overdiagnosed.

Some 22 percent of non-small cell lung cancers, the most common type of lung cancer, also represented an overdiagnosis, according to the researchers.

And 78.9 percent of the bronchioloalveolar lung cancer cases were overdiagnosed, the researchers' analysis estimated.

The problem for clinicians, the researchers acknowledged, is not being able to distinguish aggressive cancers from slow-growing ones. That’s why better markers and imaging techniques are needed, they argued, to optimize the value of screening programs.

Dr. Camidge agreed. “This study strongly makes a case for us to work on better discriminators to use when a lesion is found to help us know when to treat vs when to watch and wait,” he said.

Findings from this study were published December 9 in JAMA Internal Medicine.

The National Institutes of Health funded this research. No conflicts of interest were disclosed.

Review Date: 
December 9, 2013