Melanoma is diagnosed from a biopsy of the skin. The biopsy report contains details about your specific melanoma that will impact your treatment. While there are a number of variables listed on your report that your treating physicians may consider, the most important factors are:
Depth of invasion (Breslow depth or Breslow thickness)
- Melanoma starts in the outer layer of the skin known as the epidermis. It can grow both out from the sides (radial) or down through the layers of the skin (vertical). The deeper the melanoma grows, the higher the risk of it spreading to other areas of the body. The measurement of how far the melanoma has grown below the surface is known as the Breslow depth. Breslow depth is measured in millimeters. Melanomas can be divided in to the three main categories based on depth of invasion:
- ≤0.7 mm – Thin melanomas typically have the lowest risk profile. The likelihood of spread is extremely low.
- 0.8 – 3.9 mm – Intermediate melanomas have a variable risk of spread to nearby lymph nodes.
- ≥ 4.0 mm – Thick melanomas have the highest risk profile.
- Most of the treatment of your melanoma will be based on the Breslow depth.
- Ulceration occurs when the cells in the center of the melanoma die as the melanoma grows. This is typically seen in more aggressive forms of melanoma. Presence of ulceration is associated with higher risk.
- Mitotic rate is a measure of how fast the melanoma cells appear to be dividing under the microscope. This is assigned a numeric score. Melanomas with a score of ≥ 2 mitoses/mm2 are higher risk.
- The most common route of spread for melanoma is through the lymphatic system to nearby lymph nodes. As part of your evaluation, your treating physicians will feel for enlarged lymph nodes nearest to your melanoma. If there are enlarged lymph nodes found at the time of diagnosis, they will require biopsy. If there are no enlarged lymph nodes and the melanoma depth is ≥ 0.8 mm, your lymph nodes will be tested at the time of surgery with something known as sentinel lymph node biopsy (see Treatment Options).
- Clinical stage – Clinical stage is assigned at the time of diagnosis before the start of treatment. Clinical stage is determined by a combination of the Breslow depth, presence of ulceration, and whether or not lymph nodes are involved.
- Pathologic stage – Pathologic stage is assigned after surgery is performed for melanoma. This is the final stage on which further treatment and prognosis are based.