肿瘤发生的两阶段学说现已得到普遍公认。按照这个学说,肿瘤的发生可以分为激发(initation)和促进(Promotion)两个阶段。Be—renblum等基于下述实验结果,首先提出这一学说。如以不致引起发癌量的二甲基苯并蒽在小鼠背部皮肤涂佈一次后,接着反复涂佈巴豆油,则可在背部多处诱发肿瘤。然 The two-stage theory of tumorigenesis has now been widely recognized. According to this theory, the occurrence of tumors can be divided into two stages: initation and promotion. Be-renblum et al. first proposed this theory based on the following experimental results. For example, if dimethyl benzopyrene, which causes no cancerous amount, is applied once to the back skin of mice and then repeatedly coated with croton oil, tumors can be induced in multiple sites on the back. Natural