To classify a lung tumor, doctors often use a method called the TMN system, which is based on the tumor size (T), whether it has spread to lymph nodes (N) and metastasis to distant regions or organs of the body (M). Doctors additionally assign each letter (T, N, and M) a number, which measures how much the cancer has advanced. Larger numbers correspond to more advanced cancers. Doctors then use the TMN system to group multiple tumor types into a single staging group which allows them to provide appropriate treatment based on the severity of the cancer.

T classifications

The T classification system represents the size of the tumor.

T0: Doctors give this classification when cancer cells have been identified, but there is no visible tumor.

T1: Doctors give this classification when the tumor is smaller than 3 centimeters (1.25 inches).

T2: Doctors give this classification when the tumor is between 3 and 7 centimeters (1.25 to 2.75 inches).

T3: Doctors give this classification when the tumor is larger than 7 centimeters

T4: Doctors give this classification to tumors of any size if they have grown to invade the heart, blood vessels surrounding the heart, esophagus, or backbone.

N classifications

The N classification system represents the spread to nearby lymph nodes.

N0: Doctors give this classification when the tumor has not spread to nearby lymph nodes.

N1: Doctors give this classification when the cancer has spread to the nearest lymph nodes which reside on the same side of the body as the original lung tumor.

N2: Doctors give this classification when the cancer has spread to farther lymph nodes which reside on the same side of the body as the original lung tumor.

N3: Doctors give this classification when the cancer has spread to lymph nodes on the opposite side of the body as the original lung tumor.

M classifications

The M classification system represents the travel of the cancer to distant bodily organs.

M0: Doctors give this classification when the tumor has not traveled to distant organs.

M1a: Doctors give this classification when the cancer has traveled to the other lung, or in areas surrounding the heart.

M1b: Doctors give this classification when the cancer has traveled to distant organs like the liver, bones, distant lymph nodes, or brain.

Staging Group

Doctors use the TMN system to characterize the tumor in order to assign it to one of five staging groups. The assigned staging group will determine the prognosis and treatment the individual receives.

Stage 0

The stage 0 classification includes cancer where no tumor can be found, but where cancerous cells have been observed through other methods. It includes tumors classified in the TMN system as:

1. T0 N0 M0.

Stage I

The stage I classification includes smaller tumors that have not yet spread to lymph nodes. It includes tumors classified in the TMN system as:

1. T1 N0 M0
2. T2 N0 M0.

Stage II

The stage II classification includes tumors smaller than 7 centimeters (2.75 inches) that may have spread to nearby lymph tissue, but not to distant sites. It includes tumors classified in the TMN system as:

1. T1 N1 M0
2. T2 N1 M0
3. T2 N0 M0
4. T2 N1 M0
5. T3 N0 M0

Stage III

The stage III classification includes tumors of any size, that have begun to grow into the space between the lungs, near the heart, esophagus, or backbone. However, the tumor has not yet spread to distant organs. It includes tumors classified in the TMN system as:

1. T1 N2 M0
2. T2 N2 M0
3. T3 N2 M0
4. T3 N1 M0
5. T4 N0 M0
6. T4 N1 M0
7. T1 N3 M0
8. T2 N3 M0
9. T3 N3 M0
10. T4 N3 M0
11. T4 N2 M0

Stage IV

The stage IV classification includes tumors of any size that have spread to distant organs. It includes tumors classified in the TMN system as:

1. T(1-4) N (1-4) M1