Key Point

An early diagnostic biomarker that identifies smokers at risk for lung cancer simply by looking at the pattern of gene expression in cells may provide clinicians with a new way to manage smokers with suspected disease.

TORONTO—Looking for an early diagnostic biomarker for lung cancer that profiles gene expression in bronchial epithelial cells may directly impact the way clinicians manage smokers with suspected lung cancer, according to research conducted by Avrum Spira, MD, Associate Professor in the Departments of Medicine, Pathology, and Laboratory Medicine at Boston University, and colleagues. Used in conjunction with bronchoscopy, gene analysis can help to reliably identify patients who need immediate treatment.

We tackled a problem that we see week in and week out in our pulmonary practices smokers who were referred to us because they have an abnormality on x-ray or CT scan of the chest that indicates the possibility of lung cancer, said Dr. Spira in a presentation at the American Thoracic Societys 104th International Conference. Fiber-optic bronchoscopy which often is the initial diagnostic test can be inconclusive in early-stage lung cancer and leaves physicians with a clinical dilemma about what to do next for these patients.

Do we take them all to surgery to biopsy the lesion and be definitive in terms of what it is? That, of course, carries the risks and costs associated with a major procedure. On the other end of the spectrum, we can employ a watch and wait strategy, where we repeat a CT scan in three to six months to see if the lesion is growing and only then go to surgery. That option, of course, carries the risk that the disease will spread beyond the lung during that interval of waiting, Dr. Spira noted.

DEVELOPING THE TEST

Based on the airway field of injury hypothesis, smoke exposure affects the epithelial cells that line the entire respiratory tract at a gene expression level; the response of the individuals epithelial cell system to this exposure is associated with the risk for tobacco-induced lung cancer.

If this hypothesis is true, one could imagine developing a relatively simple tool to identify smokers at risk for having or developing lung cancer, simply by looking at the pattern of gene expression in cells that we can obtain from the large airway at the time of bronchoscopy, said Dr. Spira.

In research published in 2007, Dr. Spira and colleagues found that an 80-gene model was 83% accurate to predict lung cancer, with relatively equal sensitivity and specificity. Genes involved in turning on the immune response and cell cycle within airway epithelium functioned at higher levels in smokers with lung cancer. Genes that protect the airway epithelium from oxidative stress functioned at lower levels. Using an independent data set from Bhattacharjee et al, who profiled more than 100 specimens of normal lung tissue and lung cancer from smokers, Dr. Spira and colleagues found that their 80-gene profile could quite easily distinguish histologically normal lung tissue from lung tumors.

In that same investigation, Dr. Spira and colleagues recruited 152 subjects from four medical centers who were undergoing fiber-optic bronchoscopy for clinical suspicion of lung cancer from January 2003 to May 2005.

We did not know who had lung cancer and who did not at the time of entry into the study, Dr. Spira stressed. During the bronchoscopic procedure, millions of epithelial cells were collected from brushing the inside of the airway wall. Patients were followed for several months until a final diagnosis was made.

BRONCHOSCOPY AND GENE EXPRESSION DATA

The researchers gathered quality microarray data on 129 of the subjects and ultimately discovered that 60 had cancer; the others had benign diseases of the chest. Thirty-two of the patients with lung cancer were diagnosed at the time of bronchoscopy. Bronchoscopy is perfectly specific and never falsely diagnoses a patient with cancer; however, the sensitivity of the procedure was 53%, according to Dr. Spira. Sensitivity improved when gene expression analysis was used in conjunction with bronchoscopy.

Twenty-five of the 28 people who were missed by bronchoscopy were picked up by our gene expression study; therefore, the sensitivity increased from 53% to 95%,Ó Dr. Spira noted.

The data indicate that if patients have a nondiagnostic bronchoscopy and a negative gene expression study, there is a 95% chance that they do not have cancer, Dr. Spira said. However, if either test is positive, these patients should be taken to surgery immediately.

The gene expression biomarker identified 11 individuals as having lung cancer who did not have the disease. The researchers acknowledge that they are unsure whether these data represent false-positives or are predictions of a future event, but Dr. Spira asserted that the benefit of the negative predictive value outweighs the potential false-positives.

INTEGRATING BIOMARKER EVALUATION WITH CLINICAL FACTORS

We've shown that a combined model that includes the clinical risk factor plus the genomic biomarker is a better predictor of risk of lung cancer than either the biomarker or the clinical variables alone; that's where we ultimately think our test is going to be used together with clinical risk factors for disease, Dr. Spira noted.

We are not looking to replace the bronchoscopy. In fact, we need the test to get our samples. We really view our test as being synergistic with it, said Dr. Spira, who added that the take-home message to bronchoscopists is to continue their routine brushings and biopsies but also to spend an extra three to four minutes in the patient's right main stem bronchus and collect cells by brushing the airway epithelium there.

The pattern of gene expression in those cells will tell us something about the likelihood that that smoker has lung cancer right now. In the event that the routine cytology is nondiagnostic from the procedure, you can use the gene expression information to guide how aggressive to be in the next stages of that patient's work-up, he added.

FUTURE RESEARCH

The researchers are organizing a second larger trial to validate the results of the first trial as well as to understand if the changes seen in the airway actually precede the development of lung cancer and can be an effective screening tool for disease.

It is hard to imagine an effective mass screening tool for lung cancer that requires bronchoscopy and brushing. We do, however, believe that the airway epithelial field of injury extends to the epithelial cells that line your mouth and nose, and if that's true, we could potentially use those sites as a biomarker, Dr. Spira said.

—Lissa Edmond

Suggested Reading
Bhattacharjee A, Richards WG, Staunton J, et al. Classification of human lung carcinomas by mRNA expression profiling reveals distinct adenocarcinoma subclasses. Proc Natl Acad Sci U S A. 2001;98(24):13790-13795.
Spira A, Beane JE, Shah V, et al. Airway epithelial gene expression in the diagnostic evaluation of smokers with suspect lung cancer. Nat Med. 2007;13(3):361-366.

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