The prognosis (predicted outlook or chance of survival) of a particular cancer depends on its stage or how widespread it is in the body. Physicians treating melanoma have used several different staging systems with differing criteria. Some determinations are made based on the clinical examination, while other stage determinations are made after the biopsy is completed.

 Many types of cancer are staged using the TNM system, where:

• “T” describes the extent of a tumor’s invasion into surrounding tissues and organs.
  
  
• “N” describes whether or not the cancer has spread to surrounding lymph nodes and, if so, the size of the lymph nodes. Lymph nodes are groups of immune system filtering cells that help ward off infections and cancers. They are typically the size of a bean.
  
  
• “M” describes whether or not the cancer has metastasized or spread to distant organs.

Melanomas can be staged several ways. The major stage groups for melanoma are:

• Stage 0. The melanoma is in the epidermis but has not spread to the dermis.
  
  
• Stage I. The melanoma is localized in the skin.
  
  
• Stage II. The melanoma is still localized in the skin, but may be thicker or ulcerated.
  
  
• Stage III. The melanoma has spread to local lymph nodes.
  
  
• Stage IV. The melanoma has spread beyond local lymph nodes to distant organs, areas of the skin or lymph nodes.

According to the ACS, the 5-year survival rate for melanoma according to stage is as follow:

Another method of staging melanoma is use of the Clark’s level for diagnosis. The Clark’s classification serves to explain the anatomic level of invasion. These levels include:

• Level I. This is the earliest stage of melanoma. The lesion is still at the surface of the skin and has not invaded surrounding tissue.
  
  
• Level II. The melanoma that has gone below the epidermis (top layer of the skin) to reach the dermis (second layer of the skin).
  
  
• Level III.  The melanoma has grown down into one of the middle layers of the dermis.
  
  
• Level IV.  The melanoma has reached the bottom layer of the dermis, but not subcutaneous tissue.
  
  
• Level V. The melanoma has penetrated the top two layers of the skin and has reached the third layer.

The Clark’s classification is frequently combined with information from the Breslow’s method of classification. The Breslow classification refers to the vertical thickness of the melanoma in millimeters (mm) and is used for staging and treatment decisions. It is a more accurate prognostic indicator than the older Clark's levels.

The third method of classification is Breslow's method. The Breslow classification refers to the vertical thickness of the melanoma in millimeters (mm), which is determined during the biopsy. It is used for staging and treatment decisions.

In Breslow's method, the tumor thickness levels compare to four of the five Clark's levels:

• Up to 0.75 mm thickness compares to Clark's level II
  
  
• From 0.75 to 1.5 mm thickness compares to Clark's level III
  
  
• From 1.5 to 4.0 mm thickness compares to Clark's level IV
  
  
• Greater than 4.0 mm thickness compares to Clark's level V

The National Cancer Institute (NCI) reports that a small number of malignant melanomas spontaneously regress. At less than 1 percent of the total number of cases, these events are extremely rare.