The TNM Staging System
The TNM System (Tumor-Node-Metastasis) is the most widely used way of determining cancer stages. The TNM updated staging system, created by the AJCC (American Joint Committee on Cancer) provides important prognostic and survival information.
Codes Doctors Use to Describe Tumors
T for Tumor
The "T" categories are given numbers (from 0 to 4) based on the tumor's thickness. The tumor may also be assigned the letter "a" or "b" based on ulceration and mitotic rate.
TX: Tumor cannot be evaluated.
T0: Zero evidence of cancer.
Tis: Melanoma is "in situ" meaning it is still in the outer layer of skin and has not grown into other layers, and shows no signs of spreading.
T1: The primary tumor is 1.0 mm or thinner and one of the following:
T1a: There is no ulceration and the mitotic count is less than 1mm2.
T1b: There is ulceration or the mitotic count is equal to or greater than 1mm2.
T2: The primary tumor's thickness is between 1.01 mm and 2.0 mm and one of the following:
T2a: There is no ulceration.
T2b: There is ulceration.
T3: The primary tumor's thickness is between 2.01 mm and 4.0 mm and one of the following
- T3a: There is no ulceration.
- T3b: There is ulceration.
T4: The primary tumor is thicker than 4.0 mm and one of the following:
T4a: There is no ulceration.
T4b: There is ulceration.
N for Nodes
The "N" classification tells you if melanoma cells have moved from the primary tumor into nearby lymph nodes. (Melanoma cells that are found along the lymphatic vessel but have not yet entered a lymph node are called "in-transit metastases" or "satellites.") The number of lymph nodes to which the cancer has spread is important. When more lymph nodes have melanoma, there is reason for greater concern.
Lymph nodes are small, bean-shaped structures that are full of immune cells. They filter the blood and help fight infection.
Cancer spreads by using the lymphatic vessels that connect the lymph nodes. Often the first place that a cancer will spread will be to the closest lymph node (called the "sentinel lymph node").
NX: regional (in the area near the melanoma primary site) lymph nodes cannot be evaluated.
N0: No evidence of spread to the lymph nodes.
N1: The melanoma has spread to 1 lymph node and one of the following:
N1a: The doctor cannot feel cancer in the lymph nodes but can detect the cells when a sample is taken (microscopic metastasis).
N1b: The doctor feels cancer in the lymph node or can see it on a scan (macroscopic metastasis).
N2: Melanoma has spread to 2 or 3 lymph nodes and one of the following:
N2a: The doctor cannot feel a tumor in the lymph nodes but can see melanoma cells in a lymph node sample under the microscope (microscopic metastasis).
N2b: The doctor can feel the tumor in the lymph nodes or see it on a scan (macroscopic metastasis).
- N2c: The doctor finds in-transit metastases or satellites without finding metastatic nodes.
N3: Any of the following conditions:
The melanoma has spread to 4 or more lymph nodes.
Two or more lymph nodes appear joined together (called matted lymph nodes)
- In-transit metastases or satellites are present, with any number of affected (metastatic) lymph nodes.
M for Metastasis
The "M" classification tells you if melanoma cells have moved from the primary (original) site to distant sites in the body, and where in the body they have moved to. Usually, metastasis is used to describe the spread of a cancer into other organ systems and is associated with the more advanced stages of cancer.
The seriousness of the melanoma depends on where it has spread or metastasized to.
In melanoma, metastasis can be found in the skin, under it, or in organs like the lung, liver, or brain.
Metastases can be found in lymph nodes located beyond the primary tumor region; these are called distant lymph nodes.
Micrometastases is the term used when the cancer in the lymph nodes is not visible to the naked eye and can only be detected through a biopsy.
Macrometastases means the metastasis is large enough to be felt in a physical exam or seen by a surgeon
- Macrometastases have a more serious prognosis than micrometasteses
LDH (serum lactate dehydrogenase): A general screening test used to look for evidence of cancer in other sites of the body. LDH is an enzyme found normally in the blood in small amounts and in many body tissues. If the LDH level is high, this may indicate that there is a spread or metastasis of disease.
MX: Distant metastasis cannot be evaluated.
M0: The melanoma has not spread to distant sites.
M1a: The melanoma has spread outside the region where it first started to other parts of the skin, under the skin, or any distant lymph nodes.
M1b: The melanoma has spread to the lungs.
M1c: The melanoma has spread to any other internal organ in the body other than the lungs and the LDH is normal OR there is distant spread to any site and the LDH is elevated.
Clark Level has been replaced by mitotic count as a more accurate predictor of survival and is used in Stage I tumors no more than 1.0mm thick. However, this term may still appear on pathology reports.