While previous studies suggested that screening with low-dose spiral CT can detect lung cancers at a smaller size than chest radiography can, researchers from the Mayo Clinic in Rochester, MN, continue to be concerned about the high number of benign nodules initially reported as positive findings.

"It's very clear from our work, as well as that of others, that low-dose CT detects lung nodules and cancers when they are smaller and when they are at an earlier stage. The catch to these findings is that they don't necessarily prove that lives are being saved," said Dr. Stephen Swensen, radiology chair at the Mayo Clinic, Rochester.

Swensen and colleagues, working with a National Institutes of Health grant, screened 1520 high-risk patients who were at least 50 years old and asymptomatic. Every person in the study receives a low-dose multislice CT scan and a sputum cytology exam annually for four years. First-year results were published in the February issue of the American Journal of Respiratory and Critical Care Medicine.

One year after baseline scanning, the researchers detected 2244 uncalcified lung nodules in 1000 participants and diagnosed 25 cases of lung cancer. CT alone detected 23 cases, and sputum cytology alone detected two cases.

The mean size of the 21 non-small cell cancers detected by CT was 17 mm, and 57% were stage IA at diagnosis.

While the results indicate that low-dose CT identifies lung cancers earlier than standard radiographic imaging, researchers noted that seven benign nodules were resected along with the malignancies.

"Eighty percent of our participants have a positive finding, and the majority of those findings are false positives. As with any false-positive detection, patients now have something to worry about, and they've also got the risk of increased radiation from follow-up procedures," Swensen said.

The Mayo Clinic will participate in a multicenter, randomized, controlled lung cancer trial beginning in April to further determine whether lives can be saved through the use of low-dose CT screening.

Other researchers argue that the high false-positive rate is mainly a baseline reporting issue. According to Dr. David Yankelevitz, a Cornell University researcher working on the Early Lung Cancer Action Program trial, if researchers simply used the baseline results as guide to follow-up studies, the problem of false positives would be eliminated.

"What I'm concerned about, with all these people calling for randomized trials for lung cancer, is that we will end up with the same problem here as we have with mammography. There should be serious discussion about why this data justifies randomized trials or if these trials would even answer any of these questions," said Yankelevitz.

Swensen cautions that before routine screening can be justified, the studies must be able to provide hard numbers about whether lives are being saved.

"Today, no one should be routinely screened either with low-dose CT or chest radiography outside of a study protocol. There is no medical society that recommends screening for lung cancer with CT or chest x-ray, because these techniques are still not proven to save lives," Swensen said.

By Merlina Trevino

For more from the Diagnostic Imaging archives:

CT, MRI, CAD expand options for chest imaging
Innovations make lung screening for cancer and tuberculosis a possibility

At the CT screening crossroads: Which way will radiologists turn?
Some radiologists embrace total-body CT screening. Even critics accept specific components. The ACR opposes the concept, despite its potential to enrich its members.

CT revives interest in lung cancer screening
Trials focused on high-risk patients search for evidence of improved survival