Tumor is a general term for benign and malignant tumors. Benign tumors include benign lesions occurring in epithelial tissues (such as skin, gastrointestinal mucosa, lung and glands) and benign lesions occurring in mesenchymal tissues (such as muscle, fiber, nerve, bone lattice, fat, lymph and blood). For example, benign tumors occurring in glandular epithelium are called adenomas, and benign tumors occurring in fat are called lipomas. Malignant tumors include those occurring in epithelial tissues and those occurring in mesenchymal tissues. Those occurring in epithelial tissues are called carcinomas, and the name is the origin of the tissue “cancer”, such as those occurring in squamous epithelium are called squamous carcinomas and those occurring in glandular epithelium are called adenocarcinomas. Malignant tumors occurring in mesenchymal tissues are called sarcomas, such as osteosarcoma and liposarcoma, but not bone cancer or fatty cancer. However, benign tumors do not occur in lymphatic tissues and blood system, so once they occur, they are malignant tumors. For example, people often call: lymphoma, leukemia refers to malignant tumor.