Malignant melanoma is a tumor arising from melanocytes in the skin and other organs. Primary melanomas are caused by the proliferation of melanocytes in the epidermis and appear as heavily pigmented, progressively enlarged nodules surrounded by a red halo. Although its incidence is lower than that of basal cell carcinoma and squamous cell carcinoma, its malignancy is large, metastasis occurs early and mortality rate is high, so early diagnosis and treatment are important. It can be divided into the following four types: (1) Malignant freckle-like nevus occurs on exposed areas such as the face and neck. The cause is ultraviolet light during sun exposure. First freckles appear, which will soon turn black, and after years or decades, hard nodules and small tumors may appear on a part of this black spot. (2) Superficially disseminated type It can occur all over the body, initially flat and black, brown or a mixture of both. Sometimes part of the tumor may protrude from the skin. (3) Nodular type is a rapidly metastatic cancer that can occur in all parts of the body. The lesion site is initially hemispherical, peak-shaped, stem-like or flat and elevated. (4) Extremity freckle-like nevus type The frequency of occurrence is more than 40%, and the preferred site is the sole of the foot accounting for nearly 30%, in addition, it can also occur in the middle of the fingers, vulva and under the fingers. The size and shape of the melanocytes in the nests and the shape of the nuclei vary to varying degrees, and in aggressive melanoma, melanoma cells can be found in the dermis or subcutaneous tissue. cells.