Once the type of melanoma has been established, the next step is to classify the disease as to its degree of severity.

Classifications for melanomas are called stages. The stage refers to the thickness, depth of penetration, and the degree to which the melanoma has spread. The staging is used to determine treatment.

Early melanomas (Stages I and II) are localized, and more advanced melanomas (Stages III and IV) have spread (metastasized) to other parts of the body. There are also subdivisions within stages.

Guide to Staging
The most important factors in the staging system are the thickness of the tumor, known as Breslow's thickness, and the presence of microscopic ulceration, indicating that the epidermis covering the tumor is not intact.

Breslow's thickness measures in millimeters the distance between the upper layer of the epidermis and the deepest point of the tumor's penetration. The thinner the melanoma, the better the chance of a cure.

• In situ melanoma remains confined to the epidermis
• Very thin tumors are less than 1.0 millimeter
• Thin tumors are 1.01-2.0 mm
• Intermediate tumors are 2.0-4.0 mm
• Thick melanomas are 4.00 mm or more.

The presence of microscopic ulceration moves the tumor into a later stage, so your doctor may elect to treat such a tumor with ulceration more aggressively.

Very thin tumors are classified according to Clark's level of invasion, based on the number of layers of skin penetrated by the tumor.

• Clark's level I. The melanoma occupies only the epidermis.
• Clark's level II. The melanoma penetrates to the layer immediately under the epidermis, the papillary dermis.
• Clark's level III. The melanoma fills the papillary dermis and impinges on the reticular dermis, the next layer down.
• Clark's level IV. The melanoma penetrates into the reticular or deep dermis.
• Clark's level V. The melanoma invades the subcutaneous fat.

Sentinel Node in Diagnosis

One of the most important indicators of the severity of a melanoma is whether it has spread. The initial spread is most likely to be in the lymph node closest to the primary tumor--the sentinel node. This is identified by lymphoscintigraphy, a procedure based on injecting a small amount of radioactive substance to trace a blue dye through the lymphatic fluid. The dye is first picked up by the sentinel node. This is then excised (sentinel node biopsy) and studied in the laboratory for the presence of melanoma cells. If they are found, the other nodes in the region are also excised. If there are no melanoma cells, the other nodes are not removed.

Metastasis is a factor to be considered in all tumors more than 1.0 mm in thickness or when a thinner tumor shows evidence of ulceration.