Melanoma is a type of cancer that forms in melanocytes. Of the many different types of melanoma, most are seen in the skin (this also includes nail beds, soles of the feet, and scalp), but can be found in the eye, anal canal, rectum, and vagina. In 2002 there will be an estimated 53,600 new cases of melanoma diagnosed in the United States, accounting for about 4% of all cancers (up from 47,700 cases in 2000). The number of new cases has steadily increased for 30 years, but researchers are unsure why.
How is melanoma diagnosed and staged?
When melanoma is suspected, an excisional biopsy should be performed. This biopsy removes the lesion and the layers beneath it, allowing the depth of the lesion to be accurately determined. The depth of the lesion determines prognosis and treatment, so it is important for this to be accurate. This depth is described in two ways: Breslow thickness, which is the depth of invasion in millimeters, and Clark's level, which describes depth of invasion by the tissue it invades (levels I-V). The staging is based on these measurements, and is classified as follows:
Less then 1 mm thick.
Greater then 1 mm thick or Clark's level IV-V (invasion into reticular dermis or subcutaneous tissue).
Has spread to local lymph nodes (may or may not have known of a primary lesion) or Clark's level V (invades subcutaneous tissue).
Presents with distant metastasis (most commonly liver, lung, and brain).
All patients should have a chest x-ray and liver function studies to assess for metastases. In patients with stages II-IV, further work up for metastases is needed, including CT scan of the head and abdomen, and lymph node dissection (with or without sentinel node biopsy).