Evidence for Cancer Biomarkers in Exhaled Breath

A Review: Cancer cell growth releases molecular biomarkers into blood that can be useful in diagnostic tests, e. g., serum biomarkers. The use of serum biomarkers involves an invasive sample collection procedure. Human exhaled breath is potentially a noninvasive source of cancer biomarker compounds. A few breath analysis studies have reported sensitivities 90% and specificities >80% using a suite of exhaled breath biomarkers to differentiate cancer subjects from controls. A significant challenge for establishing breath analysis as a feasible cancer diagnostic procedure is the lack of validated diagnostic procedure. We found over 2000 breath-related studies published since circa 1900 reporting on a wide variety of breath chemical analysis methods and diagnostic findings; only a small fraction of these studies were directly related to cancer molecular biomarkers in breath. Compared to other detectors and separation techniques, mass spectrometry and gas chromatography are most suitable techniques for breath analysis. Compounds detectable in exhaled breath, with potential diagnostic utility in cancer detection, include small gaseous molecules, volatile organic compounds, proteins, and DNA. The types of cancers previously investigated using chemical analysis of exhaled breath was breast, colon, liver, lung, ovarian, and stomach cancers. Lack of multiple studies using the same breath analysis method(s) precluded meta-analysis. Our review covers the reported methods on breath analysis and assumed exhaled biomarkers. This review makes available to other researchers a catalog of published data on breath analysis for cancer detection. We make recommendations to standardize methods for more accurate breath tests in cancer detection.