Melanoma Staging

Staging is a process of finding out how widespread a cancer is. This includes describing its size as well as whether it has spread to the lymph nodes or any other organs. A staging system is a standard way of summarizing how far a cancer has spread. This helps members of the cancer care team to plan appropriate treatment and determine a patient's prognosis (outlook for survival).

The American Joint Committee on Cancer (AJCC) TNM System

The system most often used to stage melanoma is the American Joint Commission on Cancer (AJCC) TNM system. Several tests and procedures are used to assign T, N, and M categories and a grouped stage. The TNM system for staging contains 3 key pieces of information:

T stands for tumour (its size and how far it has spread within the skin). The T category is assigned a number (from 0 to 4) based on the tumour's thickness (how far down it has grown). It is also assigned a small letter "a" if it is not ulcerated and has <1 mitoses/mm2 or a "b" if it is ulcerated and/or has >1 mitoses/mm2. Ulceration means the layer of skin covering the melanoma is absent. This is seen under a microscope after a biopsy.

N stands for spread to nearby lymph nodes (small bean-shaped collections of immune system cells that help the body fight infections and cancers). The N category is assigned a number (from 0 to 3) based on whether the melanoma cells have spread to lymph nodes or are found in the lymphatic channels connecting the lymph nodes. It is also assigned a small letter: "a" if melanoma cells can only be seen with the microscope, or "b" if they can be seen with the naked eye. A letter "c" is assigned if there are very small areas of melanoma in the nearby skin or if the melanoma is in skin lymphatic channels around the tumour (but not in the nodes themselves).

The M category is based on whether the melanoma has metastasized (spread) to distant organs, which organs it has reached, and sometimes on blood levels of a substance called LDH.

There are actually 2 types of staging for melanoma:

Clinical staging

Clinical staging is done based on what is found on physical exam, biopsy of the melanoma, and any imaging tests that are done.

Pathologic staging

Pathologic staging uses all of this information, plus what is found during biopsies of lymph nodes or other organs. Therefore, the clinical stage (determined before the node biopsy) may actually be lower than the pathologic stage (determined after the node biopsy).

T Categories

The T category is based on an exam of the skin biopsy. Measuring the size and thickness of a melanoma under a microscope is believed to be the best way to determine a patient's prognosis.

The pathologist looking at the skin biopsy measures the thickness of the melanoma under the microscope with a device called a micrometer, which is like a small ruler. This technique is called the Breslow measurement. The thinner the melanoma, the better the prognosis. In general, melanomas less than 1 millimetre (mm) in depth (about 1/25 of an inch or the diameter of a period or a comma) have a very small chance of spreading. As the melanoma becomes thicker, it has a greater chance of spreading.

Another system, called the Clark level, describes how far a melanoma has penetrated into the skin instead of actually measuring it. This method has now been dropped from the latest staging system. The Clark level of a melanoma uses a scale of I to V (with higher numbers indicating a deeper melanoma) to describe whether:

  • Clark level I: the cancer stays in the epidermis
  • Clark level II: the cancer has begun to invade the upper dermis
  • Clark level III: the cancer involves most of the upper dermis
  • Clark level IV: the cancer has reached the lower dermis
  • Clark level V: the cancer has invaded to the sub cutis (fat)

The Breslow measurement of thickness is generally thought to be more useful than the Clark level of penetration in determining a patient's outlook. The thickness is easier to measure and depends less on the pathologist's judgment. But sometimes the Clark level shows that a melanoma is more advanced than doctors may think it is from the Breslow measurement.

In either system, the melanoma tends to have a worse prognosis if the pathologist says it is ulcerated (outermost covering layer of skin is absent).

Using these systems, the possible values for T are:

  • TX: Primary tumour cannot be assessed.
  • T0: No evidence of primary tumour.
  • Tis: Melanoma in situ (Clark level I - it remains in the epidermis).
  • T1a: The melanoma is less than or equal to 1.0 mm thick (1.0 mm = 1/25 or .04 inches), without ulceration and < 1 mitioses / mm2.
  • T1b: The melanoma is less than or equal to 1.0 mm thick, > 1 mitoses/mm2, and/or with ulceration.
  • T2a: The melanoma is between 1.01 and 2.0 mm thick without ulceration.
  • T2b: The melanoma is between 1.01 and 2.0 mm thick with ulceration.
  • T3a: The melanoma is between 2.01 and 4.0 mm thick without ulceration.
  • T3b: The melanoma is between 2.01 and 4.0 mm thick with ulceration.
  • T4a: The melanoma is thicker than 4.0 mm without ulceration.
  • T4b: The melanoma is thicker than 4.0 mm with ulceration.

N Categories

The possible values for N depend on whether or not a sentinel lymph node biopsy was done.

The clinical staging of the lymph nodes is listed below; it is done without the sentinel node biopsy.

  • NX: Regional lymph nodes cannot be assessed.
  • N0: No spread to nearby lymph nodes.
  • N1: Spread to 1 nearby lymph node.
  • N2: Spread to 2 or 3 nearby lymph nodes, or spread of melanoma in the skin toward a nearby lymph node area (without reaching the lymph nodes).
  • N3: Spread to 4 or more lymph nodes, or spread to lymph nodes that are clumped together, or spread of melanoma in the skin toward a lymph node area and into the lymph node(s).

Following a lymph node biopsy, the pathologic stage can be determined. The involvement of any lymph nodes can be subdivided as follows:

Any Na (N1a, N2a, etc.) means that the melanoma in the lymph node is only seen under the microscope.

Any Nb (N1b, N2b, etc.) means that the melanoma in the lymph node is visible to the naked eye.

N2c means the melanoma has spread to very small areas of nearby skin (satellite tumours) or has spread to skin lymphatic channels around the tumour (without reaching the lymph nodes).

M Categories

The M values are:

  • MX: Presence of distant metastasis cannot be assessed.
  • M0: No distant metastasis.
  • M1a: Distant metastases to skin or subcutaneous (below the skin) tissue or distant lymph nodes. Normal LDH
  • M1b: Metastases to lung. Normal LDH
  • M1c: Metastases to other organs or distant spread to any site along with an elevated blood LDH level.

Stage Grouping

Using the TNM system, a doctor will use each letter (T, N, and M) and a corresponding number. For example, a melanoma could be staged as T2, N0, M0.

To make this information somewhat clearer, several of these TNM descriptions can be grouped together into a simpler set of stages, labelled stage 0 through stage IV. This process is called stage grouping. The stage is described using 0 and Roman numerals from I to IV, and is sometimes subdivided using capital letters. In general, patients with lower stage cancers have a better outlook for a cure or long-term survival.

Stage 0: Tis, N0, M0

The melanoma is in situ, meaning that it involves the epidermis but has not spread to the dermis (lower layer). This is also called Clark level I.

Stage IA: T1a, N0, M0

The melanoma is less than 1.0 mm in thickness and Clark level II or III. It is not ulcerated, appears to be localized in the skin, and has not been found in lymph nodes or distant organs.

Stage IB: T1b or T2a, N0, M0

The melanoma is less than 1.0 mm in thickness and is ulcerated or Clark level IV or V, or it is between 1.01 and 2.0 mm and is not ulcerated. It appears to be localized in the skin and has not been found in lymph nodes or distant organs.

Stage IIA: T2b or T3a, N0, M0

The melanoma is between 1.01 mm and 2.0 mm in thickness and is ulcerated, or it is between 2.01 and 4.0 mm and is not ulcerated. It appears to be localized in the skin and has not been found in lymph nodes or distant organs.

Stage IIB: T3b or T4a, N0, M0

The melanoma is between 2.01 mm and 4.0 mm in thickness and is ulcerated, or it is thicker than 4.0 mm and is not ulcerated. It appears to be localized in the skin and has not been found in lymph nodes or distant organs.

Stage IIC: T4b, N0, M0

The melanoma is thicker than 4.0 mm and is ulcerated. It appears to be localized in the skin and has not been found in lymph nodes or distant organs.

Stage IIIA: T1a-4a, N1a or N2a, M0

The melanoma is not ulcerated. It has spread to 1-3 lymph nodes near the affected skin area, but the nodes are not enlarged and the melanoma is found only when they are viewed under the microscope. There is no distant spread. The thickness of the melanoma is not a factor, although it is usually thick in people with stage III melanoma.

Stage IIIB

T1b-4b, N1a or N2a, M0

The melanoma is ulcerated. It has spread to 1-3 lymph nodes near the affected skin area, but the nodes are not enlarged and the melanoma is found only when they are examined under the microscope. There is no distant spread.

T1a-4a, N1b or N2b, M0

The melanoma is not ulcerated. It has spread to 1-3 lymph nodes near the affected skin area. The nodes are enlarged because of the melanoma. There is no distant spread.

T1a/b-4a/b, N2c, M0

The melanoma can be ulcerated or not. It has spread to skin lymphatic channels around the original tumour, but the nodes do not contain melanoma. There is no distant spread. /t1b-4b,>

Stage IIIC

T1b-4b, N1b or N2b, M0

The melanoma is ulcerated. It has spread to 1 to 3 lymph nodes near the affected skin area. The nodes are enlarged because of the melanoma. There is no distant spread.

Any T, N3, M0

The melanoma can be ulcerated or not. It has spread to 4 or more nearby lymph nodes, to nearby lymph nodes that are clumped together, or it has spread to skin lymphatic channels around the original tumour and to nearby lymph nodes. The nodes are enlarged because of the melanoma. There is no distant spread.

Stage IV: Any T, Any N, M1

The melanoma has spread beyond the original area of skin and nearby lymph nodes to other organs such as the lung, liver, or brain, or to distant areas of the skin or lymph nodes. Neither the lymph node status nor thickness is considered, but typically the melanoma is thick and has also spread to lymph nodes.

Survival Rates by Stage

The stage of the melanoma has a major effect on a person's outlook for survival.

The 5-year survival rate refers to the percentage of patients who live at least 5 years after their cancer is diagnosed. Keep in mind that many of these patients live much longer than 5 years after diagnosis. Five-year rates are used to produce a standard way of discussing prognosis.