迄今为止,肿瘤被认为是环境因素和遗传因素两方面作用的结果。两种因素所占比重因肿瘤类型而异。遗传因素所起作用的大小称作遗传度,通常用百分数表示。遗传度越高,则提示遗传因素所起作用越大。当遗 To date, tumors are considered to be the result of both environmental and genetic factors. The proportion of the two factors varies depending on the type of tumor. The size at which genetic factors work is called heritability and is usually expressed as a percentage. The higher the heritability, the greater the effect of genetic factors. When left