Breslow thickness (also called Breslow depth) is a measurement used by pathologists to describe how far cancer cells in melanoma have grown into the skin. Melanoma is a type of skin cancer that starts in cells called melanocytes, which are normally found in the top layer of the skin (the epidermis).
This measurement tells doctors the distance from the surface of the skin to the deepest point where melanoma cells are seen. It helps determine how serious the melanoma is and is one of the most important factors used to decide the tumour stage (called the pathologic tumour stage or pT).
Why is Breslow thickness important?
The deeper the cancer cells go into the skin, the more likely the melanoma is to metastasize (spread) to other parts of the body. A thin melanoma has a better prognosis (outcome) than one that has grown deeper. For this reason, Breslow thickness is used to help decide on further treatment, follow-up, and whether additional tests (such as a sentinel lymph node biopsy) are needed.
How do pathologists measure Breslow thickness?
Pathologists measure Breslow thickness using a microscope. The measurement starts at the top layer of the skin, specifically from the surface of the granular layer of the epidermis (or from the base of any ulcer if the top layer is missing), and goes down to the deepest point where melanoma cells are found. The result is usually given in millimetres (mm).
When is Breslow thickness reported?
If only a small piece of the tumor was removed during the first procedure (called a biopsy), a preliminary Breslow thickness may be included in the pathology report. However, the most accurate measurement is made after the entire melanoma has been removed. This final measurement is used to determine the tumour stage.
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