Any skin samples taken by a biopsy or an excision are sent for microscopic examination, and a pathology report is issued by the pathologist or dermatopathologist, (a pathologist who specializes in skin biopsies.) The pathology report further describes many aspects of the melanoma, including the type, the depth of invasion, the tissue level of invasion, the presence or absence of a lymphatic response, ulceration, regression, satellite lesions, and blood/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 is one in which the cancer cells spread within the subcutaneous skin tissue in the site of the original tumor. These lesions are often called "in-transit metastases."

Some Terms You May See on Your Pathology Report

 Cellular Description (the type of melanoma):

• Superficial spreading melanoma

• Nodular melanoma

• Acral lentiginous melanoma

• Lentigo melanoma

• Other: mucosal melanoma

Breslow Depth: Measures in millimeters how thick the primary tumor is, regardless of its anatomic layer. It is measured from the top layer of the skin to its deepest level.

Clark Level: An older way to classify how invasive the melanoma is. Clark Level was replaced in 2010 by more reliable predictive features (mitotic rate and ulceration) and it is likely that pathologists will eventually stop including it on their pathology report. It describes how deeply the primary tumor has penetrated the different levels of the skin. The higher the level number, the deeper the level of skin it has penetrated.

• Clark Level I-lesion involves the dermis
• Clark Level II-lesion involves the papillary dermis
• Clark Level III-lesion invades and fills the papillary dermis
• Clark Level IV-lesion invades reticular dermis
• Clark Level V-lesion invades subcutaneous tissue

(Depending upon where the melanoma is located on the body, the millimeters of depth for each Clark level can vary widely, so one person's Clark III may be 1 mm, while another person's is 2 mm.)

Radial Growth Phase (RGP): The melanoma lesion is described as either having RGP present or absent. If present, RGP indicates that the melanoma is growing horizontally, or radially, within a single plane of skin layer.

Vertical Growth Phase (VGP): The melanoma is described as either having VGP present or absent. If present, it 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 looks for the number of lymphocytes within the lesion. This response, or TILs, is usually described as brisk, nonbrisk, or absent, although occasionally it can be described as mild or moderate. TILs indicate the immune system's ability to recognize the melanoma cells as abnormal. Some studies suggest that the presence of increasing number of TILs may be associated with a better prognosis.

Ulceration: Ulceration is the sloughing of dead tissue. This can sometimes occur in the center of a melanoma lesion. The presence of ulceration may alter 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. Whether or not a lesion is considered to have ulceration is determined by a pathologist when they review the biopsy under the microscope.

Regression: Regression is described as being present or absent. If it is present, the extent of regression is identified. Regression describes an area within the melanoma where there is an absence of melanocytic growth. When regression is present, the total size of the melanoma is hard to characterize.

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 is reported as the number of mitoses per mm². (example ≤1 mitoses/mm²). A high mitotic count means more tumor cells are dividing at a given time, and is one of the criteria used to stage a melanoma. A higher count is associated with a worse prognosis.

Satellites: Satellite lesions are nodules of tumor/melanoma located more than 0.05 mm from the primary lesion. Satellites are described as being present or absent. The presence of satellite lesions usually indicates a poorer prognosis.

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, respectively, and is associated with more aggressively growing melanomas.