A diagnosis of lung cancer is usually confirmed after samples collected during biopsies or other testing procedures are sent to a pathology lab for analysis. The pathologist examines the samples under a microscope to determine whether cancer is present, and if so, the specific type of cancer. This is done through what is called “immunohistochemistry”, a process by which the samples are treated with special proteins or antibodies designed to attach only to a specific substance found in certain cancer cells. If a patient’s cancer contains that substance, the antibody will attach to the cells.
Until now, blood tests have not been used to diagnose lung cancer, but rather, to get a sense of a patient’s overall health. Recently, however, scientists have identified patterns of abnormal molecules called microRNA (miRNA) in the plasma of lung cancer patients, and have determined that it might be possible to use these patterns to detect lung cancer in a blood sample. The patterns may be detectable for up to two years before detection is possible via computed tomography (CT scan), and therefore may have strong predictive, diagnostic and prognostic potential.
The abnormal patterns were initially discovered in tissue samples collected from patients who were participating in a clinical trial examining the possible benefits of using spiral CT scans to screen at-risk individuals for lung cancer. The trial involved 1,035 people over 50 years of age who had smoked at least a pack of cigarettes a day for more than 20 years. Patients underwent CT scans annually for five years and provided blood, sputum and urine samples for testing.
Researchers first analyzed 28 lung tumor samples and 24 samples of normal lung tissue for their MiRNA profiles, and through this process identified miRNAs that could discriminate between tumor tissue and normal tissue. Additionally, they found patterns of miRNAs that distinguished tumors with faster growth rates and that were also associated with poor disease-free survival. The scientific team then analyzed blood samples that had been collected more than a year before an individual’s lung cancer was detected by spiral CT. They found a signature of 15 miRNAs that could identify 18 of 20 individuals whose cancer was later detected by CT. To verify these findings, the signature was applied to a second set of blood samples obtained during a similar but unrelated lung cancer trial. In this case, the signature identified 12 of 15 patients whose lung cancer was diagnosed by CT at a later date.
Based on these findings, researchers concurred that circulating miRNA in plasma is detectable well before clinical detection is possible by spiral CT. They are hopeful that in the not too distant future, high-risk individuals can be identified through a simple blood test on the basis of miRNA profiling.
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