Breslow thickness: meaning and melanoma staging

Thickness, not diameter

Diameter is the visible width of a spot on the skin. Breslow thickness is a vertical microscopic measurement; it cannot be determined from a photograph or measured at home with a ruler.

How it is measured

The pathologist measures from the reference surface layer of the epidermis to the deepest invasive tumour cell. With ulceration, measurement starts at the base of the ulcer. An incomplete specimen can limit the measurement, so the report must be interpreted as a whole.

Why it matters

Thickness contributes to the melanoma T category and clinical decisions, alongside ulceration and other findings. It does not determine the overall stage by itself. Older “level” groupings with survival percentages are not an appropriate way to estimate an individual’s risk.

Questions about your report

• What is the thickness, and is the measurement complete?
• Is ulceration present?
• What does this mean for my care?

Understanding Breslow thickness in your report

Breslow thickness, also called Breslow depth or Breslow index, describes how deeply an invasive melanoma extends into the skin. The result is reported in millimetres after a pathologist examines tissue removed by biopsy or surgery. It is one part of the report, not a diagnosis that can be made from the appearance of a mole.

Breslow thickness versus Clark level

Breslow gives a numerical depth; Clark level names the anatomical skin layer reached. A result in millimetres cannot be converted directly into a Clark level. Neither measurement alone tells you whether melanoma has reached lymph nodes or distant organs.

Does a thickness measurement tell me my stage?

No. In the TNM system, thickness helps describe the primary tumour (T). Ulceration is also relevant, while N and M describe regional and distant spread. Read more about melanoma staging and prognosis before interpreting a number in isolation.

A practical way to discuss the result

For example, “Breslow thickness 0.7 mm” describes a tissue measurement; it is not “stage 0.7” or a personal survival prediction. This is an illustrative example, not a treatment recommendation. Ask whether the report includes ulceration and whether the entire depth could be assessed. Your team uses the complete findings to explain further surgery, possible staging tests and follow-up.