Mucinous epidermis-like carcinoma is a common parotid malignant tumor from parotid duct epithelium, mainly composed of epidermis-like cells, mucinous cells and intermediate type cells (basal-like cells). According to the histological characteristics, it is divided into two types: highly malignant (hypo-differentiated) and hypo-malignant (highly differentiated). In highly malignant cases, epidermal-like cells and intermediate type cells are predominant, while in low-grade malignant cases, differentiated mature mucous cells and intermediate type cells are predominant, but it is difficult to distinguish strictly between these two types, and intermediate type cells can differentiate into epidermal-like cells or mucous cells. The tumor is variable with or without envelope, so it often infiltrates into the surrounding tissues without clear boundary. Adenoid cystic carcinoma, also known as cylindrical adenocarcinoma and cylindrical tumor, is a more common type of salivary gland malignant tumor, but it is not common in parotid gland. The cancer cells are mainly glandular epithelial cells, which resemble the basal cells of the epidermis and are polygonal in shape, often forming clusters or trabeculae of different sizes. The masses and trabeculae are separated by a dense fibrous interstitium and become lobulated. The adenoid vesicles contain mucus, and the fibrous tissue between the tumor cells has glassy changes. 3.Malignant mixed tumor and mixed tumor malignant transformation Most scholars believe that malignant mixed tumor is derived from benign mixed tumor malignant transformation, pathology can be seen partly as benign mixed tumor structure, partly as adenocarcinoma, squamous carcinoma, or undifferentiated carcinoma lesion at the same time, between the two can be seen benign lesion to malignant lesion migratory transformation part. Malignant mixed tumors present as basal cell-like cells or pleomorphic cell-like cells. The carcinoma has an incomplete or absent envelope and grows slowly for several years or even more than 10 years. Microscopic findings of microscopic foci of necrosis and hemorrhage, dystrophic calcification and stromal ossification, vitreous changes and marginal infiltrative growth in mixed tumors should be considered as signs of malignancy. Adenocarcinoma, also known as non-specific adenocarcinoma, refers to malignant tumors with varying degrees of histological glandular differentiation, but cannot be classified as a certain histopathological type. The cancer cells may be derived from the reserve cells of the intercalary ducts. It usually occurs in the parotid gland as an irregular, hard mass, usually without an envelope and without clear demarcation from the surrounding tissue. The adenocarcinoma has a complex histomorphology with undifferentiated polygonal cells or highly differentiated cylindrical cells with more pronounced anisotropy. The adenocarcinoma cells are arranged into tubular or adenoid structures, and sometimes the ducts expand to form microcysts containing mucous secretions. 5.Alveolar cell carcinoma accounts for 7.2% to 19% of malignant tumors of parotid gland. It occurs mostly in the superficial lobe and caudal part of parotid gland, and is a low grade malignant tumor with little local destructiveness. The tumor is hard in texture, the surface is not smooth, lobulated, and although there is an envelope, it is thin, but some are incomplete, and cancer cells can be seen infiltrating within the envelope. The cancer cells consisted of different types of tumor cells such as alveolar-like cells, intercalary duct-like cells, vacuolar cells, clear cells and non-specific glandular cells. The cancer cells are large, polygonal, rich in cytoplasm, granular or vacuolated, with rounded, small, centered nuclei and rare splitting images. 6.Squamous cell carcinoma often occurs in the malignant transformation of mixed tumors, sometimes it is a squamous cell carcinoma or low differentiation type mucous epidermis-like carcinoma that originates from the ducts, which is still inconclusive. It is a highly malignant tumor, which is mostly derived from ductal epithelial squamous cell metaplasia.