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Staging is the process used by doctors to evaluate how far the cancer has spread. Staging is an important factor in making treatment decisions and also plays an important role in helping doctors predict the chance of recovery (prognosis).

The classification system used for staging patients with non-small cell lung cancer (NSCLC) is called the TNM staging system. The TNM staging system takes into consideration the following three major variables:

• T = Tumor Size - the size of the tumor is graded on a scale of 0 to 4.

• N = Node Involvement - the extent of lymph node involvement is graded on a scale of 0 to 3.

• M = Metastases (spread of the tumor to distant organs) - graded on a scale of 0 to 1. A score of "0" indicates no metastases while a score of "1" indicates that that the tumor has metastasized.

The TNM scores are then grouped together to classify the extent of the disease into one of the following 4 Stages:

• Stage I - the tumor is localized (confined) to the lung

• Stage II - The tumor has spread to nearby lymph nodes or it has spread to the chest wall, diaphragm, mediastinal pleura (the membrane that covers the outside of the lungs near the heart), or the parietal pericardium (the outer membrane of tissue that covers the heart). Stage II is further subdivided into Stage IIA and Stage IIB based on the size of the tumor and whether or not it has spread to the regional lymph nodes.

• Stage III - The tumor has spread to the lymph nodes in the mediastinum (the space within the chest located between the lungs that contains the heart, major blood vessels, trachea, and esophagus) OR the tumor has spread to the lymph nodes on the opposite side of the chest or in the lower neck. Stage III is further subdivided into Stage IIIA and Stage IIIB.

• Stage IV - The cancer has spread to other parts of the body or to another lobe of the lung.