癌包括一组由多种因素单独或联合作用而引起的疾病。这些因素不但在外环境,也在宿主体内起作用。许多研究说明,大量的各种化学和生物学致癌因素可与一定的组织和器官的癌肿有因果关系。致癌因素可以起附加、联合或抑制作用。被调查人群中癌危害的差异首先反映出环境状况的不同,其次反映出遗传感受性的不同。靶组织的年龄、性别和生理状况也影响癌的发病率。 Cancer includes a group of diseases that are caused by multiple factors alone or in combination. These factors not only work in the external environment but also in the host body. Many studies have shown that a large number of various chemical and biological carcinogenic factors can have a causal relationship with a certain tissue and organ cancer. Carcinogenic factors can play an additive, combined, or inhibitory role. The difference in cancer risk among the investigated population first reflected the difference in environmental conditions, and secondly it reflected the different genetic susceptibility. The age, sex and physiological condition of the target tissue also affect the incidence of cancer.