Lung cancer is currently the most frequently diagnosed major cancer in the world and the most common cause of cancer mortality world- wide. This is largely due to the carcinogenic effects of cigarette smoke. Over the coming decades, changes in smoking habits will greatly influ- ence lung cancer incidence and mortality throughout the world. These changes may also impact upon the histological types of lung cancer. Tumour classification is important for consistency in patient treat- ment, and because it provides a basis for epidemiologic and biologi- cal studies. The previous WHO classification...