Skin samples taken by a biopsy or surgical excision are typically sent to a pathologist/pathology laboratory for microscopic examination and diagnosis. A pathology report is issued by the pathologist or dermatopathologist. The pathology report states the diagnosis and further describes many aspects of the appearance of the melanoma, including the type, depth of invasion, tissue level of invasion, presence or absence of a lymphatic response, presence or absence of ulceration, mitotic count, presence or absence of regression, presence or absence of satellite lesions, and presence or absence of blood vessel/lymphatic vessel/nerve invasion.

Additionally, the pathology report will describe whether the excised lesion is a primary melanoma, in which case it would be described using the terms above, or a metastatic melanoma deposit. A metastatic melanoma deposit is one in which the melanoma started somewhere else on the skin and some of the melanoma cells broke off and spread within the skin tissue to the current biopsy/specimen site.

Some Terms You May See on Your Pathology Report

Type of Melanoma (Histologic Subtype):

  • Superficial spreading melanoma
  • Nodular melanoma
  • Acral lentiginous melanoma
  • Lentigo melanoma
  • Desmoplastic melanoma
  • Other: mucosal melanoma
  • Other: uveal melanoma

Breslow Depth: Measurement in millimeters of how thick the primary tumor is, regardless of its Clark Level. It is measured from the top layer of the skin to its deepest point.

Clark Level: Clark Level was replaced in the revised melanoma staging system in 2010 by more reliably predictive features (mitotic count and ulceration). It is now only used to stage thin melanomas (< 1mm).

Radial Growth Phase (RGP): The melanoma lesion is described as either having RGP present or absent. If present, RGP is an indication that the melanoma is growing horizontally, or radially, within a single plane in the upper/superficial skin layers (mainly in the epidermis).

Vertical Growth Phase (VGP): The melanoma is described as either having VGP present or absent. If present, VGP is an indication that the melanoma is growing vertically, or deeper, into the tissues.

Tumor-Infiltrating Lymphocytes (TILs): TILs describe the patient’s immune response to the melanoma. When the pathologist examines the melanoma under the microscope, he/she looks to see whether or not there are lymphocytes within the melanoma. The amount of lymphocyte invasion/response to the melanoma is described as brisk (a lot of lymphocytes), nonbrisk (some), sparse (few) or absent (none), although occasionally it can be described as mild or moderate. TILs appear to indicate that your immune system has recognized the melanoma cells as abnormal and is trying to move into the melanoma to attack it. Some studies suggest that the presence of increasing number of TILs may be associated with a better prognosis.

Ulceration: Ulceration is described as being present or absent. It is the breakdown or loss of the top layer of cells in a melanoma and often occurs in the center of a tumor. The presence of ulceration increases the stage classification of a melanoma. Ulceration is thought to reflect rapid tumor growth, leading to the death of cells in the center of the melanoma and thus is associated with a worse prognosis. The pathologist can determine whether ulceration is present or absent when they review the biopsy under the microscope.

Regression: Regression is described as an area of the tumor without active melanoma cell growth and is described as present or absent. If it is present, the extent of regression is estimated.. When regression is present, the measured thickness of the melanoma may not be the greatest/true thickness.

Mitotic Count (Mitotic Rate): Mitosis is the process by which one mature cell divides into two identical cells. When pathologists study a melanoma, they will count the number of actively dividing cells that they see. Averaging this number gives the mitotic count and it is reported as the number of mitoses per square millimeter (mm2), (example ≤1 mitoses/mm2). A high mitotic count means more tumor cells are dividing at a given time, and is associated with a worse prognosis.

Satellites: Satellite lesions are small nodules of tumor/melanoma located more than 0.05mm from the primary lesion, but less than 2cm. Satellites are described as being present or absent. Some satellite lesions (macroscopic) can be seen with the naked eye. Others, which are smaller (microscopic) can be found only by the pathologists. Both macroscopic and microscopic lesions are reported in the pathology report.

Blood Vessel/Lymphatic Invasion: Blood vessel invasion, also called angioinvasion, or lymphatic vessel invasion, is described as being present or absent. If present, it means that the melanoma has invaded the blood or lymph system and is associated with more aggressively growing melanomas.

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