After a melanoma has been diagnosed, the “level” and “stage” will be determined.
The prognosis of melanoma and the treatment options available depend on the stage at which the cancer is diagnosed.
One of the most common areas of confusion is the difference between the levels of melanoma and the staging of melanoma. The level of melanoma relates to the depth of the melanoma in the skin and the staging of melanoma refers to how limited or advanced the melanoma is at the time of diagnosis.
The stages of melanoma are determined by reviewing different features including;
Tumour depth or thickness is measured in millimetres by a pathologist using a microscope. This is referred to as the ‘Breslow Depth’. The thicker the tumour, the greater the chance it might have metastasised (spread) to regional lymph nodes or distant sites. Thinner melanomas have a better prognosis.
|Less than 1mm:||Thin melanoma|
|1-4 mm:||Intermediate melanoma|
|Greater than 4mm:||Thick melanoma|
The tumour depth can also be described using a ‘Clark level’ to indicate the number of layers of skin penetrated by the melanoma. The Clark level is a number from I-V with V being the deepest penetration of the skin.
Ulceration of a skin tumour means that the epidermis (or top layer of the skin) that covers the melanoma is not intact. Ulceration may not be seen with the naked eye. Ulcerated melanomas pose a greater risk for metastatic progression.
Mitotic count refers to the number of cancer cells that are in the process of dividing when tissue is examined microscopically. Mitotic rate is usually measured as number of mitoses per mm2. Higher mitotic rates (eg those greater than 5 mm2) indicate more rapid activity and a faster division of cells and a more aggressive melanoma type.
Lymph node activity
A biopsy of the involved lymph node is taken and examined by a histopathologist to determine if the node tests positive for melanoma.
Presence of distant metastases
Further investigations (including scans and ultrasounds) can determine if the melanoma has spread (metastasised) to distant sites in the body including organs, bones and the brain.
Stages of Melanoma
In Stage 0 melanoma, the malignant tumour is still confined to the upper layer of the skin (epidermis or Level I). This means that the cancer cells are only in the outer layer of the skin (epidermis) and have not grown any deeper. The term for this is in situ, which means ‘in place’ in Latin. There is no evidence the cancer has spread to the lymph nodes or distant sites.
In Stage I melanoma there is no evidence the cancer has spread to lymph nodes or distant sites (metastasis). Stage IA can be defined as a melanoma that is less than or equal to 1mm in thickness without ulceration. Stage IB can be defined as a melanoma that is either less than or equal to 1mm in thickness with ulceration or between 1.01mm and 2mm in thickness without ulceration.
In Stage II melanoma there is no evidence the cancer has spread to lymph nodes or distant sites (metastasis). There are three subclasses of Stage II: IIA, IIB, IIC. Stage IIA can be defined as a melanoma that is greater than 1mm but less than on equal to 2mm in thickness with ulceration or between 2.01 and 4mm in thickness without ulceration. Stage IIB can be defined as a melanoma that is between 2.01mm and 4 mm in thickness with ulceration or greater than 4mm in thickness without ulceration. Stage IIC can be defined as a melanoma that is greater than 4mm in thickness with ulceration.
Stage III melanoma is defined by the presence of lymph node involvement along with ulceration in the skin melanoma. For Stage III melanoma, the depth of the melanoma no longer matters. There is no evidence the cancer has spread to distant sites (metastasis). There are three subclasses of Stage III Melanoma: IIIA, IIIB, IIIC. The subclasses relate to the size and number of lymph nodes that contain the melanoma cells.
Stage IV melanoma occurs when the melanoma has spread beyond the original site and regional lymph nodes to more distant areas of the body. The blood level of LDH (serum lactate dehydrogenase) in the patient may or may not be elevated. The most common sites of metastasis are to vital organs (lungs, abdominal organs, brain, and bone) and distant lymph nodes (lymph nodes beyond the primary tumour region).
*Staging of Melanoma is not to be confused with Clark Levels classification of Cutaneous Melanoma.