Cross-sectional studies have investigated exhaled biomarkers as a function of disease, both as biomarkers of disease state and as predictive markers. In cross-sectional studies, a control group is compared with a patient or diseased group, and breath markers are analyzed to identify qualitative or quantitative differences between the two groups. Phillips and coworkers [14] investigated alveolar gradients (i.e., the abundance in breath minus the abundance in room air) of C4 to C20 alkanes and monomethylated alkanes in the breath as tumor markers in primary lung cancer. They concluded that a breath test for C4 to C20 alkanes and monomethylated alkanes provided a rational new set of markers that identified lung cancer in a group of patients with histologically confirmed disease. The analytical methodology was described in 2003 , where it was reported that amongst smokers and ex-smokers there was a sensitivity for malignancy of 86% (55/64) and a specificity of 83% (19/23). This compared with sensitivity and specificity in non smokers of 66% (2/3) and 78% (14/18). Overall therefore the VOC breath test was not affected by smoking status.