Once cancer is diagnosed, a physician determines the stage of the cancer. Melanoma is categorized into one of five main stages (0 through IV). The size, location and whether the melanoma has spread are used to determine the stage.
Melanoma is usually staged twice. First, a physician will consider the results of the patient’s physical exam and any imaging tests that were done, and assign a clinical stage. Then, after a biopsy or surgical procedure, a pathologist will examine tissue taken from the tumor (and possibly nearby lymph nodes) and assign a pathologic stage. The second staging is more precise and is the key to deciding treatment options.
Both the clinical and pathologic stages of melanoma are classified according to the tumor, node, metastasis (TNM) system developed by the American Joint Committee on Cancer (AJCC) (see Table 2).
The first classification of the primary melanoma in the TNM system is for the thickness of the tumor (T). Each T classification is further divided into groups according to whether ulceration (a break in the outer layer of skin over the melanoma) is absent (subcategory a) or present (subcategory b). For example, a non-ulcerated melanoma 3 millimeters (mm) thick is classified as T3a, whereas an ulcerated melanoma 2 mm thick is classified as T2b. Another factor for thin melanomas (less than 1 mm thick) is the mitotic rate, which measures how fast the cancer cells are dividing and multiplying.
The node (N) classification is used to describe how many lymph nodes contain melanoma cells. The N category includes subcategories to describe the number of cancer cells in the lymph nodes. If the cancer cells in the nodes can be seen only with a microscope, the metastasis (spread) is considered to be microscopic (a). If enough cancer cells are in the lymph node that the doctor can feel the mass during a physical exam or can see the mass on an X-ray, it’s said to be “macroscopic” lymph node involvement (b). Another subcategory (c) indicates whether melanoma has spread to the lymphatic vessels leading to a lymph node. This is known as “in-transit melanoma,” which is metastatic melanoma found between the original tumor and the nearby cluster of lymph nodes.
The metastasis (M) category is used to classify the melanoma according to whether the cancer has spread beyond the region where the melanoma started to distant sites.
Once the melanoma is classified according to the TNM system, an overall stage of disease is assigned (see Table 1). Stage I and II melanomas are considered to be local (or localized) disease. Stage III melanoma is referred to as regional disease, and Stage IV is known as distant metastatic or advanced disease.