Lung fluid test may predict lung cancer risk

By Joene Hendry

NEW YORK (Reuters Health) - Testing lung fluid samples for levels of surfactant protein D (SP-D), which is thought to have a protective effect on the lungs, may help identify patients with a high risk of lung cancer, Canadian researchers report.

"The only proven way to cure lung cancer is to detect it early," lead author Dr. Don D. Sin, of the University of British Columbia in Vancouver, told Reuters Health. Finding a method to predict who will and will not develop lung cancer would permit screening for high-risk patients and initiation of therapies to reduce lung cancer risk, he noted.

To this end, Sin and colleagues measured SP-D levels in 71 individuals (72 percent male) who participated in a lung cancer prevention study, the researchers report in the medical journal Chest. Low levels of SP-D in lung fluid have been associated with abnormal or precancerous cells, referred to as "dysphasia."

The study group consisted of former and current (73 percent) smokers with bronchial dysplasia. The patients underwent bronchoscopy, a diagnostic procedure that inspects the windpipe and lungs, at the start of the study and 6 months later. All of the patients received inhaled budesonide therapy to lower their risk of lung cancer.

Sin's group compared changes in SP-D from fluid collected during these bronchoscopy tests to determine if changes in SP-D levels correlated with bronchial dysplasia progression.

Their findings indicate that for each one-unit decrease in SP-D levels, the risk of disease progression increased by more than 3-fold. A single unit reduction in lung fluid SP-D levels over 6 months increased the participants' risk of disease progression by 76 percent, the investigators report.

Over the 6-month period, the investigators also noted reductions in SP-D levels that were associated with increases in levels of oxidized glutathione, a marker of oxidative stress, which is believed to be involved in the lung cancer development. Declines in SP-D levels also correlated with the number of pack-years of smoking and reduced lung function.

Because SP-D levels appear important in the development and progression of lung cancer, testing for changes in SP-D may help predict lung cancer risk, the researchers note.

The investigative team recommends additional studies to determine whether blood test for SP-D and other molecules may also help identify patients at high risk for lung cancer.

SOURCE: Chest, September 2008.