Test For Early Detection of Asbestos-Linked Lung Cancer
There's hope for an early-detection test that could improve survival for people with a deadly cancer linked to asbestos exposure, scientists report.
High blood levels of a protein called osteopontin are linked to the development of pleural mesothelioma, an asbestos-related cancer that invades the chest cavity and the lining of the lungs, say scientists reporting in the Oct. 13 issue of the New England Journal of Medicine.
"The earlier you detect it, the better the chance that you can do therapy that impacts survival," said study author Dr. Harvey Pass. He did the work while at Wayne State University, in Detroit, and is now professor of surgery at New York University School of Medicine.
There is currently no way to screen for mesothelioma, a potential hazard for the 7.5 million American workers with a history of workplace exposure to asbestos. Those people include foundry workers, miners, shipbuilders and an estimated 1.5 million maintenance and construction workers. The challenge is to single out those who will develop the cancer from those with other asbestos-related lung conditions.
Eventhough the work is preliminary, osteopontin levels may point to heightened mesothelioma risk, Pass said. The findings are based on a study of 190 people -- 69 with nonmalignant asbestos-related disease, 76 with mesothelioma and 45 smokers with no exposure to asbestos.
Blood tests showed that the levels of osteopontin rose along with years of asbestos exposure -- the lowest levels were in people exposed to asbestos for less than 10 years, while levels doubled for people with more than 10 years of exposure and increased steadily with asbestos-caused damage to the lungs.
Blood concentrations of osteopontin were six times normal levels in people with mesothelioma, even during the early stages of the disease, the scientists found.
A blood marker that helped doctors catch the disease early could offer patients real hope, Pass said. "If you find that this marker of risk is high, you can take action, starting with CT scanning to detect the disease early," he noted.
But that optimism was not echoed by Dr. Mark R. Cullen, a professor of medicine and public health at Yale University, who wrote an accompanying editorial.
Longer survival through early detection has been shown in breast cancer, colon cancer and some other malignancies, Cullen said, but the evidence for it in mesothelioma is weak. It is possible that detecting an inevitably fatal cancer early gives the illusion of longer survival, since the time after diagnosis is longer than if the tumor is detected closer to death, he noted.
And the osteopontin test has a major weakness, Cullen said. It lacks specificity, which means it also detects other, less fatal conditions, putting those patients through testing that might be unnecessary.
Nevertheless, he said, "I strongly encourage this kind of research in the hope that a number of good things might come of it -- an early blood test, a very good diagnostic test, and hopefully over the next few years a breakthrough in treatment.".
Pass is continuing his work, which is funded by a grant from the National Cancer Institute (NCI). In fact, his NYU facility has been designated a "biomarker laboratory" by the NCI, he said.
Pass and colleagues will soon start screening banked blood samples from mesothelioma patients. That and future studies will aim at determining the exact levels of osteopontin that could be used in a screening test.
"If we find the same relationship with banked serum [blood] -- something that should take two years -- and if the marker holds up, then we can proceed to a prospective trial to see if it finds mesothelioma early," he said.
About 2,500 cases of mesothelioma are reported in the United States each year, Pass said, eventhough he believes the cancer might be underdiagnosed because there is no official registry for it. Only 5 percent of cases are detected early, Pass said. The life expectancy for those diagnosed late is just nine to 12 months.
However, detected early, mesothelioma "does respond to therapy," he said. Treatments include radiation therapy, chemotherapy and surgery.