Higher lung cancer risk seen in asbestos-exposed smokers

Nov 27, 2004

CHICAGO - Asbestos was banned from most industrial uses more than a decade ago, but its grim legacy is just beginning to unfold in humans. Over the next five to 30 years, doctors are bracing for sharply increased rates of lung cancer, mesothelioma, and other lung problems in people who were exposed to airborne asbestos fibers over prolonged periods.

For those who also smoked, the risk of lung cancer is expected to be exponentially higher than that of the general lung cancer screening population, in whom bronchogenic carcinomas have been found at rates between 1.1% and 2.7%. Clinical data among higher-risk individuals has been scarce.

Just how common is lung cancer among asbestos-exposed smokers? High but not astronomical, according to a new study from Germany. In Sunday's lung cancer screening sessions at the RSNA meeting, radiologists aimed to assess lung cancer risk in 178 former power plant workers exposed to asbestos, nearly all of whom were also smokers or former smokers.

"In our population we were looking at 10% of almost 2,000 people who were working at power plants -- the top 10% who were at the highest risk of developing lung cancer," said radiologist Dr. Marco Das from the University of Aachen.

The mean age of the 178 patients was 67 years (range 55-77 years), with a mean asbestos exposure time of 29.65 years (range 16-45 years). Eighty-seven percent of the patients were smokers, 12% former smokers, and 1% nonsmokers.

Das and colleagues acquired low-dose MDCT images of the chest on a Somatom Sensation 16 scanner (Siemens Medical Solutions, Forschheim, Germany) at 16 x 0.75-mm collimation, 120 kVp, 10-20 mAs depending on body weight, and rotation time 0.5 seconds. The images were double-read by two experienced radiologists on a PACS workstation, and further corroborated with the aid of Siemens' LungCARE CAD software.

"In our results we found five lung cancers (one small cell lung cancer, three squamous cell carcinomas, one adenocarcinoma), which were all confirmed at histology from CT-guided biopsy," Das said. This leads to a malignancy rate of 2.8%. Three cases were early stage disease, and two were advanced, he added.

Three cases of suspected lung cancers were shown to be false-positive at biopsy; inflammatory disease was diagnosed in all three.

Asbestos-related changes such as asbestosis, pleural plaques, or fibrosis were seen in 80 patients. But the high prevalence of noncalcified nodules was perhaps the most dismaying result, as it indicates a need for extensive follow-up.

In addition to the five lung cancers, the researchers also found a whopping 353 lung nodules in the group -- an average of two per patient -- with an average diameter of 5.4 mm. Only 10% of these nodules were calcified, and only 28 patients had no lung nodules. Eighty patients with nodules 5 mm and smaller (n = 212) underwent follow-up CT at one year, Das said. For nodules ranging from 5-10 mm (n = 135), patients were followed up at three months.

So far the group has found no new bronchogenic cancers at follow-up, but 23 new nodules, all 5 mm or smaller, have appeared.

"We found a high malignancy rate of 2.8% at baseline screening," Das concluded. "We detected an extensively large number of pulmonary nodules which have to be followed."

Dr. John Mayo, associate professor of radiology at the University of British Columbia in Vancouver, commented after the talk on the enormous task ahead for lung cancer screeners. "We find that we're drowning in nodules -- and some of them grow," he said.

By Eric Barnes
AuntMinnie.com staff writer
November 28, 2004

Part I: The back story on asbestos x-ray B readers, September 7, 2004

Part II: A survey of asbestos-related imaging, September 7, 2004

Study sounds alarm over integrity of expert readers' testimony, August 6, 2004

Separating inflammation from malignancy on thoracic FDG-PET, April 9, 2004