肿瘤是机体细胞在内外致瘤因素长期作用下，发生过度增生及分化异常而形成的新生物。肿瘤的分类原则，首先应根据其组织发生和生物学特性，并结合其发生部位和形态学特征。肿瘤可以生长在机体的任何部位，几乎所有组织都可以发生肿瘤，且各具有不同性质，因此种类繁多。一个合 Tumors are new organisms formed by abnormal proliferation and differentiation of body cells under the long-term effects of internal and external tumorigenic factors. The principle of tumor classification should first be based on its histogenesis and biological characteristics, combined with its site of occurrence and morphological characteristics. Tumors can grow in any part of the body. Tumors can occur in almost all tissues, and each has a different nature and therefore a wide variety. A joint