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长期以来,人们一直认为人体每天均有大量的新的肿瘤细胞产生,并由此推论出机体内可能存在着一个强有力的免疫监视或自然抵抗系统。这些系统以各种不同机制杀灭体内不断产生的大量肿瘤细胞。而老年人的高癌发病率也被认为是由于免疫系统功能下降而使部分癌细胞获得免疫”逃逸”。但目前人们已认识到,每一机制所杀灭的肿瘤细胞群是有限的,因此这些机制不可能在长时期内每天杀伤大量的新生瘤细胞。此外,有证据表明当某些重要的自然抵抗和免疫监视
For a long time, people have been thinking that the human body has a large number of new tumor cells every day, and thus inferred that there may be a strong immune surveillance or natural resistance system in the body. These systems kill a large number of tumor cells that are constantly being produced in the body by various mechanisms. The high incidence of cancer in the elderly is also thought to be due to the weakening of the immune system, so that some cancer cells get immune “escape.” But now people have realized that the tumor cell population killed by each mechanism is limited, so these mechanisms cannot kill a large number of new tumor cells every day for a long period of time. In addition, there is evidence that when some important natural resistance and immune surveillance