Lung cancer is divided into two main categories: non-small cell lung cancer (NSCLC, 80% of the cases) and small cell lung cancer (SCLC, 16% of the cases). NSCLC is further classified into adenocarcinoma (40%), squamous cell carcinoma, and large cell carcinoma (15%). SCLC occurs almost exclusively in smokers. SCLC also distinguishes several histologic groupings: pure small cell, or mixed small cell, and large cell carcinoma.
SCLC is usually more aggressive than NSCLC with its rapid doubling time, high growth fraction, and the early development of metastases.
Metastases usually occur in bones, liver, adrenal glands, pericardium, brain, and spinal cord.
Staging for NSCLC is done using the internationally accepted TNM (tumor, node, metastasis) staging system. Until now SCLC is divided into limited and extensive disease stages, but probably the staging system as for NSCLC will be adopted in the next years.