Skin tumors are a large group of diseases including: epidermal tumors, tumors of the skin appendages, skin cysts, soft tissue tumors and verrucous lesions of the skin, peripheral nerve tumors, melanocytic tumors, tumors of the cutaneous lymphoid reticulum and hematopoietic system, and metastatic skin tumors. Common malignant tumors of the skin: 1. Non-melanoma skin cancer NMSC: Basal cell carcinoma BCC, squamous cell carcinoma SCC 2. Malignant melanoma MM 3. Primary lymphoma and sarcoma of the skin 4. Cutaneous manifestations of systemic tumors A. Basal cell carcinoma (BCC): BCC is the most common skin cancer, which is invasive and destructive. Epidemiology: The age of onset is mostly >40 years old, male >female, and the incidence rate of BCC is about 500-1000/100,000 people in the United States. The incidence of BCC in the United States is about 500-1000 per 100,000 people. 85% of BCCs appear in the head and neck region, and about 25%-30% of BCCs occur in the nose alone. Early manifestations of BCC are: localized skin slightly raised, yellowish or pink nodules of the size of a pinhead or a green bean, translucent nodules, hard, thin epidermis, accompanied by capillary dilatation, but no pain or tenderness. If the lesion is located in the deeper layers of the epidermis, the surface skin is slightly concave, losing the luster and texture of normal skin. After a few months or years, the lesion site manifests scaly flakes, and later repeated crusting, flaking manifestation of ulceration and blood seepage. When the lesion continues to increase in size, a superficial ulcer is formed in the middle, and its edge may be elevated and jagged like worm-eaten. Clinical classification of basal cell carcinoma (BCC): nodular type, superficial type, pigmented type: need to be distinguished from pigmented nevus, malignant black, etc. Ulcerated type: higher malignancy, sclerotic type (scar type): high malignancy, easy to metastasize in distant places. B. Squamous cell carcinoma (SCC): SCC is a malignant tumor originated from keratinocytes of the epidermis or appendage, which is more frequent in old people and preferred to occur in the exposure area. It is divided into: squamous carcinoma in situ (Bowen’s disease), invasive squamous carcinoma (highly differentiated squamous carcinoma, lowly differentiated squamous carcinoma) Histopathologic grading of SCC