Changes in breath VOC patterns are independent of the size of the lung cancer in that T1 tumours (<3cm) have a similar breath pattern of abnormality to T4 tumours, raising the possibility that VOC abnormalities may even be detectable at the preneoplastic (severe dysplasia or carcinoma in situ) stage. It describes a comparison between 212 controls without lung cancer and 195 patients with primary lung cancer. The breath test was as likely to be abnormal in stage 1 disease as in stage 4 disease. This implies firstly that as a screening tool VOC breath testing has potential to detect operative curable cases. Secondly, it implies that oxidative changes leading to altered breath VOCs are an early feature of lung cancer development, and that the method may therefore detect the presence of preneoplastic lesions in the bronchial tree.