The Breslow thickness (or Breslow depth) is used to describe how far tumour cells in a type of skin cancer called melanoma have traveled from the surface of the skin into the tissue below. This measurement helps doctors predict how the tumour will behave. It is used to determine the tumor stage for most types of skin cancer.
The surface of the skin is called the epidermis. The tissue directly below the epidermis is called the dermis. Melanoma starts in the epidermis on the surface of the skin. The movement of tumour cells from the epidermis into the tissue below is called invasion.
The Breslow thickness is measured from the surface of the skin to the deepest point of invasion. It is usually reported in millimetres (mm). A preliminary measurement may be given after a small tissue sample is removed in a procedure called a biopsy. A final measurement will be made after the entire tumour has been removed and examined by a pathologist under the microscope.