2/3的癌症难以避免

Two thirds of cancers are unavoidable even if you live a healthy life, a study has shown. , ,研究表明 ，即使生活方式健康
，依然有三分之二的癌症是难以避免的。, ,Scientists in the US found cancers are caused by random ¹ mistakes in the genetic ² code that occur when cells divide. , ,The findings challenge the widespread view that cancer mutations are generally inherited or triggered by environmental factors. , ,Instead, the vast majority of cancers are probably down to unlucky defects in replicating ³ DNA ⁴ that occur out of the blue, they suggest. , ,Lead scientist Dr Cristian Tomasetti, from Johns Hopkins Kimmel Cancer Center in the US, said: "It is well-known that we must avoid environmental factors such as smoking to decrease our risk of getting cancer. , ,"But it is not as well-known that each time a normal cell divides and copies its DNA to produce two new cells, it makes multiple mistakes. , ,"These copying mistakes are a potent ⁵ source of cancer mutations that historically have been scientifically undervalued, and this new work provides the first estimate of the fraction of mutations caused by these mistakes." , ,The research, published in the journal Science, indicates that almost two-thirds of cancer-causing mutations are due to DNA copying errors.