In lung cancer, the stage of the disease at the time of diagnosis is a major factor in determining how to treat the cancer, and how long the patient can expect to live. In general, survival is longest for patients with very early-stage disease and shortest for patients with very advanced disease that has spread to several areas of the body. However, some groupings with very different clinical features can have similar prognosis. Staging is based on the results of physical and surgical examinations, and laboratory and imaging tests, including biopsies.
To determine the stage, medical professionals first categorize each tumor by size and by how far it has extended. This identification method is called the TNM system.
The TNM categories then determine the stage (numbered 0 to IV) of the cancer.
The International Association for the Study of Lung Cancer recently revised the non-small cell lung cancer staging system in 2009. Extensive analysis was performed on an international database. The major staging categories remain the same, while additonal subgroupings within the T, N, and M descriptors were added.
The TNM System
TNM stands for Tumor, regional lymph Nodes, and Metastasis (cancer spread beyond the original tumor).
T refers to the size and spread of the tumor. In TX and T0, the tumor is either unable to be assessed or indicated by cancer cells in sputum or lung samples but it cannot be seen.
Tis: Carcinoma in situ. The cells are cancerous, but the tumor does not show evidence of spreading.
In T1, the tumor is 3 cm or less in size, is still contained in the lung or the membrane covering the lung, and has not reached the main airway. In T1a, the tumor is less than or equal to 2 cm and in T1b, the tumor is greater than 2 cm but less than or equal to 3 cm in diameter.
In T2, the tumor has one or more of the following features:
- It is greater than 3 cm or less than 7 cm
- It involves the main airway
- It is 2 cm or more away from the ridge (the carina) at the lowest part of the windpipe
- It has invaded the pleura
- It is associated with collapsed lung tissue (atelectasis) or swelling that blocks part (but not all) of the lung
T2 is further broken down in the new staging system. T2a refers to a tumor greater than 3 cm but less than or equal to 5 cm in diameter. T2b is greater than 5 cm but less than or equal to 7 cm.
In T3, a tumor is greater than 7 cm or has directly invaded any of the following:
- Chest wall
- Membrane covering organs and structures in the chest
- Outer wall of the membrane around the heart (pericardium)
In addition, one or more of the following conditions are present:
- The tumor is in the main airway, less than 2 cm away from the carina, but is not in the trachea (windpipe).
- The tumor is associated with a collapsed lung or swelling that blocks the entire lung.
In T4, the tumor has invaded any of the following:
- Area between the lungs (mediastinum)
- Great vessels (the blood vessels that carry blood from the heart)
- Carina, trachea, or esophagus
- Main portion of the spine
In addition, one or both of the following occurs:
- Separate tumors are present in the same lobe
- The tumor is accompanied by an increased amount of fluid between the pleural membrane and the lung.
N followed by a number from 0 to 3 refers to whether the cancer has reached regional (in the area of tumor) lymph nodes.
- In stage N0, the regional lymph nodes are still cancer-free.
- In N1, the cancer has spread to the nearest lymph nodes around the airways, to the hilum (a central zone in the lung where blood and lymph vessels enter), or both. The tumor has extended directly into lymph nodes within the lung.
- In N2, the cancer has spread to lymph nodes in the middle of the chest next to the affected lung, to the nodes below the carina, or to both regions.
- In N3 the cancer has spread to lymph nodes in the middle of the chest that are next to the opposite lung, to the hilum in the opposite lung, to lymph nodes in nearby or opposite muscle tissue, or to lymph nodes above the collar bone.
M Stages refer to cancer spread (metastasis).
- In M0, spread has not occurred.
- In M1a, tumor nodules are present in the other lung or on the pleura (the sac surrounding the lungs), or a malignant pleural effusion (cancer cells in the fluid within the pleura) is present.
- In M1b, distant spread has occurred.
Other Factors Determining Treatment Choices and Outcome
Staging factors are used to help determine treatment and outlook. The following suggest a more aggressive disease:
- The presence of respiratory symptoms
- A tumor larger than 3 cm
- High numbers of blood vessels in the tumor
Researchers are always looking for more accurate ways to determine lung cancer treatment and outlook. For example, some research involves specific biomarkers and related blood vessel development within tumors. These markers might eventually help predict the cancer's aggressiveness and determine the best treatment approach.
Using the information, lung cancer is divided into stages, I through IV. Stages I through III, are further divided into A or B (for example stage IA and IB). Each stage will usually have a different approach to treatment.