Do Positive Cancer Results Need to Be Redefined?

Lung cancer CT scan positive results examined for nodules of varying sizes

(RxWiki News) At what point should tests be considered positive for cancer? This may sound like a silly question. Physician scientists, however, don’t have a solid answer when it comes to lung cancer.

Currently, doctors want to perform more tests on any lung nodule that’s five millimeters (about the size of half a pencil eraser) or larger. Further testing on five millimeter lesions often results in a “false positive” – a test result that shows cancer that is actually not present. Testing and “work-up” for diagnosing lung cancer involves surgery, which can be harmful.

A recent study looked at the benefits and harms of diagnosing larger lung tumors measuring six to nine millimeters to learn if standards need to be redefined.

"Ask your doctor if you need to be screened for lung cancer."

The Multi-institutional International Early Lung Cancer Action Program study involved 21,136 participants who had a baseline (initial) computed tomography (CT) lung cancer screening scan between 2006 and 2010. Claudia I. Henschke, PhD, MD, of the Department of Radiology at Mount Sinai School of Medicine, led the study.

The goal of the study was to see how often positive results and possible delays in diagnosis occurred when CT scans screened for nodules six to nine millimeters in size.

Here’s what the study found:

  • 16 percent of CT scans produced positive results when using the current definition of 5.0 millimeters.
  • 10.2 percent were positive for 6.0 millimeter nodules; using this standard would have reduced workup by 36 percent.
  • 7.1 percent were positive for nodules 7.0 millimeters; 56 percent workup reduction.
  • 5.1 percent were positive for 8.0 millimeters; 68 percent reduction in further tests.
  • 4.0 percent were positive for 9.0-millimeter nodules; 75 percent fewer tests.

If these alternative values had been used, then diagnosis would have been delayed by nine months at most for 0 percent of individuals with six-millimeter nodules; 5 percent for patients with seven-millimeter lesions; 5.9 percent for eight-millimeter nodules and 6.7 percent for individuals with nine-millimeter nodules.

The authors noted that since this was a retrospective (past) analysis, it was not possible to determine if delayed diagnosis changed patient outcomes.

“These findings suggest that using a threshold of 7 or 8 mm to define positive results in the baseline round of computed tomography screening for lung cancer should be prospectively evaluated to determine whether the benefits of decreasing further work-up outweigh the consequent delay in diagnosis in some patients,” the authors wrote.

"The key point of this article is that the definition of positive result needs to be continually prospectively evaluated and updated in light of emerging evidence from ongoing screening programs to reduce unnecessary surgery for nonmalignant pulmonary nodules and reduce potential harms of the diagnostic work-up, while maximizing the diagnosis and treatment of curable cases of lung cancer," the authors concluded.

This study was published February 18 in the Annals of Internal Medicine. The research was funded by Flight Attendant Medical Research Institute and the American Legacy Foundation.

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Review Date: 
February 18, 2013