Detection of Lung Cancer With Volatile Markers in the Breath

Michael Phillips, MD, Renee N. Cataneo, MA, Andrew R.C. Cummin, DM, Anthony J. Gagliardi, MD, FCCP, Kevin Gleeson, MD, Joel Greenberg, BS, Roger A. Maxfield, MD, FCCP, and William N. Rom, MD, MPH, FCCP

Disclosures

CHEST. 2003;123(6) 

In This Article

Abstract and Introduction

Study Objectives: To evaluate volatile organic compounds (VOCs) in the breath as tumor markers in lung cancer. Alkanes and monomethylated alkanes are oxidative stress products that are excreted in the breath, the catabolism of which may be accelerated by polymorphic cytochrome p450-mixed oxidase enzymes that are induced in patients with lung cancer.
Design: Combined case-control and cross-sectional study.
Setting: Five academic pulmonary medicine services in the United States and the United Kingdom.
Patients and Participants: One hundred seventy-eight bronchoscopy patients and 41 healthy volunteers.
Intervention: Breath samples were analyzed by gas chromatography and mass spectroscopy to determine alveolar gradients (ie, the abundance in breath minus the abundance in room air) of C4-C20 alkanes and monomethylated alkanes.
Measurements: Patients with primary lung cancer (PLC) were compared to healthy volunteers, and a predictive model was constructed using forward stepwise discriminant analysis of the alveolar gradients. This model was cross-validated with a leave-one-out jackknife technique and was tested in two additional groups of patients who had not been used to develop the model (ie, bronchoscopy patients in whom cancer was not detected, and patients with metastatic lung cancer [MLC]).
Results: Eighty-seven of 178 patients had lung cancer (PLC, 67 patients; MLC, 15 patients; undetermined, 5 patients). A predictive model employing nine VOCs identified PLC with a sensitivity of 89.6% (60 of 67 patients) and a specificity of 82.9% (34 of 41 patients). On cross-validation, the sensitivity was 85.1% (57 of 67 patients) and the specificity was 80.5% (33 of 41 patients). The stratification of patients by tobacco smoking status, histologic type of cancer, and TNM stage of cancer revealed no marked effects. In the two additional tests, the model predicted MLC with a sensitivity of 66.7% (10 of 15 patients), and it classified the cancer-negative bronchoscopy patients with a specificity of 37.4% (34 of 91 patients).
Conclusions: Compared to healthy volunteers, patients with PLC had abnormal breath test findings that were consistent with the accelerated catabolism of alkanes and monomethylated alkanes. A predictive model employing nine of these VOCs exhibited sufficient sensitivity and specificity to be considered as a screen for lung cancer in a high-risk population such as adult smokers.

Primary carcinoma of the lung is the leading cause of cancer death in both men and women in the United States.[1] A total of 99,000 men and 78,000 women are affected every year, and 86% of them are dead within 5 years of diagnosis. However, with early detection and treatment, the 5-year survival rate improves dramatically from 20% in patients with stage 3 lung cancer to 70% in patients with stage 1 disease. Researchers therefore have sought screening tests to detect lung cancer in its earliest stages, and several promising new early markers have been proposed, including computer-assisted image analysis of chest radiographs, polymerase chain reaction based assays of sputum, fluorescence bronchoscopy, and spiral CT scanning.[2,3,4]

In 1971, Pauling et al[5] reported a new method for the microanalysis of breath that revealed the presence of large numbers of previously undetected volatile organic compounds (VOCs) in normal human breath. It is now known that a sample of breath contains, on average, approximately 200 different VOCs, mostly in picomolar (ie, 10-12 mol/L) concentrations.[6] We and others[7,8,9,10] have identified apparent new markers of lung cancer among these VOCs, which are predominantly alkanes and methylated alkanes. Until recently, these were empirical observations that could not be readily explained by known pathophysiologic processes. However, a plausible explanation has now emerged from an improved understanding of the mechanisms and kinetics of VOC synthesis and clearance. Alkanes and methylated alkanes in the breath are apparent mark-ers of oxidative stress, which are the toxic effects of reactive oxygen species comprising oxygen free radicals and hydrogen peroxide. Reactive oxygen species are constantly produced in the mitochondria and leak into the cytoplasm where they cause peroxidative damage to proteins, polyunsaturated fatty acids, and DNA.[11,12] Peroxidative changes to DNA bases may be carcinogenic,[13,14] and oxidative stress appears to be increased in some cancers,[15] although the evidence for a causal role is lacking. Lipid peroxidation of polyunsaturated fatty acids in cell membranes generates alkanes such as ethane and pentane, which are excreted in the breath,[16] and breath methylalkanes may be products of the same process.[17] Alkanes are metabolized to alkyl alcohols by cyto-chrome P450 (CYP)-mixed oxidase enzymes,[18] and a number of studies[19,20,21,22] have demonstrated that these enzymes are activated in lung cancer. Polyaromatic hydrocarbons in tobacco smoke induce the activity of CYP 1A1 in the lung and placenta, and CYP 1A2 in the liver, resulting in the accelerated metabolism of a number of drugs and the activation of some procarcinogens.[23] These findings provide a rational basis for a breath test for lung cancer. The activation of CYP enzymes in patients with lung cancer may accelerate the degradation of volatile alkanes and monomethylated alkanes that are produced by oxidative stress and result in measurable changes in the composition of the breath.

We have recently reported tests for the set of C4 to C20 alkanes and their monomethylated derivatives in the breath, which appear to vary with the amount of oxidative stress.[17,24] These breath VOCs were significantly more abundant in older than in younger healthy humans, a finding that is consistent with previous reports[25,26] that aging is accompanied by increased oxidative stress. We report here an evaluation of this breath test as a marker of disease in patients with lung cancer.

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