Lung cancer is now the most frequent cause of cancer mortality in both men and women in the UK and US.Its incidence is continuing to rise worldwide, in particular in developing countries, where smoking is increasing.
It is estimated that 80% of cancer deaths are due to smoking. The risk of lung cancer relates to the number of cigarettes smoked, the number of years of smoking, early age of starting to smoke, and the type of cigarette (greater risk with unfiltered and high-nicotine).
While health education has had some success in reducing tobacco consumption in men, smoking in women and adolescents is increasing. Much less frequent causes of lung cancer are exposure to:
♦ Polycyclic aromatic hydrocarbons
♦ Inorganic arsenicals
There is evidence that lung cancers may arise in pluripotent stem cells in the bronchial epithelium, and this would certainly offer an explanation for the mixed histology that is fairly commonly seen. The WHO pathological classification is: A Squamous cell carcinoma (30%) B Small cell carcinoma (20%) C Adenocarcinoma (40%):
For the purposes of management, lung cancers are grouped as non-small cell (NSCLC) or small cell (SCLC), but within the former certain patterns of disease do relate to histological subtype. For example, squamous cancers typically arise in proximal segmental bronchi and grow slowly, disseminating relatively late in their course. Adeno-carcinomas are often peripheral in origin and even small resectable lesions carry a risk of occult metastases.
However the risk of dissemination is greatest in SCLC, where it is estimated that >90% of patients have either overt or occult metastases at presentation. These aggressive tumours most frequently arise in large airways but can rarely present as a small peripheral nodule. Some have suggested that the latter presentation is in fact indicative of a different pathology with an inherently better prognosis.
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