Lung cancer kills more Americans than any other cancer. Doctors know that smokers and former smokers are at much greater risk than the rest of the population, yet there's no safe way to screen them, and lung tumors are rarely discovered in early, more curable stages.

Now researchers at a Gaithersburg, MD, pharmaceutical company say they have found that 99 percent of patients with all stages of lung cancer have detectable levels of a particular protein in their blood that healthy individuals do not. The company, Panacea Pharmaceuticals, is reporting encouraging preliminary results for its test for the protein this week at a conference of the American Association for Cancer Research. The company is working toward federal approval to market the test for high-risk patients.

"Lung cancer is the only major cancer with no approved screening procedure," points out David Carbone, director of Vanderbilt University's Vanderbilt-Ingram Cancer Center's research program in lung cancer. Smokers and former smokers have a ten- to fiftyfold greater risk of developing lung cancer. But "there's no way to detect [lung cancer] before they're coughing up blood and suffering shoulder pain," signs of advanced cancer, says Carbone.

Screening patients with no symptoms using CT scans is expensive and dangerous. The screens have a high rate of false positives, which means that some patients are subjected to lung biopsies and other harrowing and risky procedures that may turn out to be unnecessary. Carbone cites a recent study showing that one-fifth of patients diagnosed with lung cancer who had part of their lungs surgically removed didn't have cancer at all.

"There is a dramatic need for an effective screening strategy," says Carbone. A blood test could help doctors make better decisions when the results of a CT scan are unclear. If the company's results hold up in independent testing and long-term, in-depth studies, Panacea's test could meet this need.

The Panacea test detects a protein called HAAH. "We found we could detect it as early as stage one, when the symptoms are first presented," says Mark Semenuk, a research scientist with the company. According to Panacea, HAAH can be detected using a commonplace laboratory technique for identifying proteins in the blood.

The HAAH protein's potential as a cancer biomarker was first explored by Jack Wands, the director of Brown Medical School's Liver Research Center and a consultant to Panacea. Wands has been studying the protein's role in cancer for six years. It's made by healthy cells, which do not release it into the blood. But cancer cells make the protein in very large quantities, carry it on their surfaces, and release it into the blood. Its function in cancer cells is now "quite clear," says Wands. The protein has an important role in molecular pathways that make cells become more mobile, which enables tumors to grow and spread throughout the body.