Lung cancer is grouped into stages, based on the size of the tumor and whether it has spread to other areas of the body. The staging system helps doctors determine the best treatment and further monitoring. Staging uses a TNM classification (Tumor, Nodes, Metastases).

The T part of the TNM system has 4 stages:

• In stage T1, lung cancer is only present in the lung and is less than 3 cm in size.
• In stage T2, the cancer is confined to the lung, but is larger than 3 cm.
• In stage T3, the lung cancer has spread outside the lung to the chest wall, pleura, diaphragm or pericardium.
• In stage T4, the cancer has spread to the esophagus, trachea or heart, or elsewhere in the lung.

Stage M (metastases) determines whether the cancer has spread to distant areas of the body. The groups are:

• M0: no distant spread
• M1: distant metastases to other organs

Stage N (nodes) classifies any spread to the local lymph nodes. The groups are:

• N0: no local lymph node involvement
• N1: nodes involved on the same side as the tumor
• N2: nodes in the mediastinal area on the same side as the tumor
• N3: nodes involved in other areas