Malignant melanoma is a tumor arising from melanocytes in the skin and other organs. Cutaneous melanoma presents as pigmented skin lesions that change significantly over months or years. Although its incidence is low, its malignancy is high, metastasis occurs early, and mortality is high, so early diagnosis and treatment are important. Most malignant melanomas occur in adults, and cases of giant congenital pigmented nevi with secondary cancer are mostly seen in children. A (Asymmey) represents asymmetry, B (Borderirregularity) represents border irregularity, C (Colorvariegation) represents color diversification, D (Diameter>6mm) represents diameter greater than 6mm, E (Elevation, evolving) represents lesion elevation and progression. If the lesions meet the ABCDE criteria, malignant melanoma is highly suspected and a biopsy is needed for histopathological examination to further confirm the diagnosis. However, some subtypes, such as nodular melanoma, cannot be determined by ABCDE criteria. Histopathology Melanocytes proliferate abnormally and form nests of cells within the epidermis or at the epidermal-dermal boundary. These nests vary in size and may fuse with each other. There are varying degrees of variability in the size and shape of the melanocytes within the nests, as well as in the shape of the nuclei. Mitosis (including abnormal mitosis) is more common than in benign pigmented nevi, and pigment granules are present in the cytoplasm of the tumor cells. In aggressive malignant melanoma, tumor cells grow infiltrating into the dermis or subcutaneous tissue. Immunohistochemical staining: tumor cells were positive for S100, positive for HMB45 and positive for MelanA. Pathological grading 1. Invasion depth grading Clark (1969), after studying the relationship between invasion depth of melanoma and prognosis, classified melanoma into 5 grades according to invasion depth. The higher the grade, the worse the prognosis. Grade I: Tumor cells are confined to the epidermis above the basement membrane. Grade II: The tumor cells break through the basement membrane and invade the papillary layer of the dermis. Grade III: Tumor cells fill the dermal papillae and invade further down, but not to the dermal reticular layer. Grade IV: The tumor cells have invaded the dermal reticular layer. Grade V: The tumor cells have passed through the dermal reticular layer and invaded into the subcutaneous fat layer. 2, vertical thickness grading Breslow (1970) studied the relationship between vertical thickness of melanoma and prognosis, and classified melanoma into 5 grades according to the thickest part of melanoma (thickness from the granular layer to the deepest part of the melanoma) measured by eye-microscope: less than 0.75 cutaneous malignant melanoma, 0.76-1.50 cutaneous malignant melanoma, 1.51-3.00 cutaneous malignant melanoma, 3.01-4.50 cutaneous malignant melanoma, 3.01-4.50 cutaneous malignant melanoma, 3.01-3.00 cutaneous malignant melanoma. 3.01 to 4.50 cutaneous malignant melanoma and greater than 4.50 cutaneous malignant melanoma. The greater the thickness, the worse the prognosis was found to be. This microscopic grading method, which has since been widely adopted, has proven to be of great value in determining prognosis.