Early diagnosis of lung cancer is critical, as most cases are already inoperable at the time of diagnosis, and thus bear a grave prognosis. With increasing knowledge of the genetic aspects of lung cancer, the field has also experienced an increasing number of potential markers that might serve in the detection of changes in the lung epithelium that predispose to cancer (reviewed inrefs.1 –3 ). Of these, oncogene mutations were among the first genetic biomarkers to be studied extensively, since they fulfill many criteria that link theirde novoappearance to the process of field cancerization (4 ). Oncogene mutations of theras- andp53-type are found in chronic smokers and patients with preneoplastic and neoplastic lesions but almost never in normal lung (4 ). In animal models carcinogens present in tobacco smoke have been shown to induce typical G-T transversions that lead to missense mutations (5 ). Moreover it has been shown that smoking leads to particular types of mutations, many of which are concentrated in particular hot spots, thus making it plausible that the same spectrum also arises in man on continuous exposure to tobacco carcinogens.
