Classification, staging and prognosis of lung cancer.

Lung cancer has increased in incidence throughout the twentieth century and is now the most common cancer in the Western World. It has a poor prognosis, only 10-15% of patients survive 5 years or longer. Outcome is dependent on clinical stage and cancer cell type. Lung cancer is broadly subclassified on the basis of histological features into squamous cell carcinoma, adenocarcinoma, large cell carcinoma and small cell carcinoma. The histopathological type of lung cancer correlates with tumour behaviour and prognosis. Staging based on prognosis is essential in clinical trials comparing different management strategies, and enables universal communication regarding the efficacy of different treatments in specific patient groups. The anatomic extent of disease determined either preoperatively using imaging supplemented by invasive procedures such as mediastinoscopy, and anterior mediastinotomy or following resection are described according to the T-primary tumour, N-regional lymph nodes, M-distant metastasis classification. The International System for Staging Lung Cancer attempts to group together patients with similar prognosis and treatment options. Various combinations of T, N, and M define different clinical or surgical-pathological stages (IA-IV) characterised by different survival characteristics. Refinements in staging based on imaging findings have enabled clinical staging to more accurately reflect the surgical-pathological stage and therefore more accurately predict prognosis. Recent advances including the use of positron emission tomography in combination with conventional staging promises to increase the accuracy of staging and therefore to reduce the number of invasive staging procedures and inappropriate thoracotomies.