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 random¹ mistakes in the genetic² code that occur when cells divide.

美国科学家发现，细胞分裂时产生的基因序列随机错误能致癌。、

The findings challenge the widespread view that cancer mutations are generally inherited or triggered by environmental factors.

这一发现之前，人们普遍认为，细胞癌变通常是遗传或者环境因素所致。

Instead, the vast majority of cancers are probably down to unlucky defects in replicating³ DNA⁴ that occur out of the blue, they suggest.

然而，研究人员指出，大部分癌症的发生可能都是DNA复制时突然产生的错误所致。

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.

美国约翰霍普金斯大学金墨尔癌症中心首席科学家克里斯蒂安•托马塞蒂博士指出：“众所周知，我们必须避开吸烟等环境因素从而减少罹癌的可能。”

"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.

“但是，很多人不知道的是，每当一个正常的细胞分裂并复制DNA从而产生两个新细胞时，会发生各种各样的错误。”

"These copying mistakes are a potent⁵ 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."

“这些细胞分裂时产生的错误是导致癌基因变异的重要原因，但是，一直以来，这种观点在科学领域都未受到足够重视。这是第一次有研究猜测认为，癌基因的变异可能源于细胞分裂时产生的错误。”

The research, published in the journal Science, indicates that almost two-thirds of cancer-causing mutations are due to DNA copying errors.

这项发表在《科学》期刊上的研究表明，将近三分之二的致癌基因突变可能源于DNA复制时产生的错误。

The discovery helps explain why cancer often strikes people who follow all the rules of healthy living and have no family history of the disease.

这一发现有助于解释为何罹癌的通常是那些生活方式健康且无家族病史的人。

Cancers triggered by copying errors could occur "no matter how perfect the environment", according to co-author Dr Bert Vogelstein, also from the Johns Hopkins Kimmel Cancer Center.

同样来自美国约翰霍普金斯大学金墨尔癌症中心的伯特•沃格斯坦博士是本次研究论文的共同著者，他表示，“不管外部环境多么无可挑剔”，由基因复制错误导致的癌症都有可能发生。

He said: "We need to continue to encourage people to avoid environmental agents and lifestyles that increase their risk of developing cancer mutations.

他还提到：“我们要继续鼓励人们避开那些增加癌基因变异风险的环境因素和生活方式。”

"However, many people will still develop cancers due to these random DNA copying errors, and better methods to detect all cancers earlier, while they are still curable, are urgently needed."

“不过，很多人仍会因为DNA复制时随机产生的错误患上癌症，因此，我们现在急需找到更好的方法及早检测出所有癌症，在它们还可以治愈时发现它们。”

The team studied mutations that drive abnormal cell growth in 32 different types of cancer.

研究人员对32种癌症中导致细胞异常生长的变异原因进行了研究。

Using DNA sequencing and epidemiological data, they developed a mathematical system of assessing the role of genetic copying errors in cancer.

研究人员利用DNA测序和流行病学资料，建立了数学模型，以此评估基因复制时随机产生的错误在罹癌中起到的作用。

The results showed that it generally took two or more critical gene mutations to trigger cancer.

研究结果表明，一般情况下，癌症的发生至少需要两种关键基因的变异。

In some cancer types, such as those affecting the prostate, brain and bone, more than 95% of the harmful mutations were due to random DNA copying errors.

在部分癌症种类中，例如前列腺癌、脑癌和骨癌等，至少95%的有害突变是DNA复制时随机产生的错误所致。

Copying mistakes were linked to 77% of pancreatic cancers but only 35% of lung cancers, which were mostly triggered by smoking and other environmental factors.

虽然77%的胰腺癌和DNA复制时产生的错误有关，但是，这种错误造成的肺癌比例仅为35%，吸烟等环境因素才是引起肺癌的主要原因。

Overall, 66% of cancer mutations resulted from copying errors, 29% from lifestyle or environmental factors, and just 5% from inherited faulty genes⁶.

整体而言，在引起细胞癌变的众多原因中，细胞分裂时产生的错误占比66%，生活或环境因素占比29%，异常基因遗传占比仅为5%。

The researchers compared DNA copying errors to "typos" in a written manuscript.

研究人员将细胞分裂错误比作书稿上的“打字错误”。

"You can reduce your chance of typographical errors by making sure you're not drowsy⁷ while typing and that your keyboard isn't missing some keys," said Dr Vogelstein.

沃格斯坦博士表示：“打字的时候我们可以通过确保自己意识清醒、键盘上的键没有缺漏，来减少拼写错误。”

"But typos will still occur because no-one can type perfectly⁸."

“但是，打错字的情况仍会出现，毕竟，谁也做不到一字不错。”

Professor Mel Greaves, director of the Centre for Evolution and Cancer at The Institute of Cancer Research in London, said: "Even if, as this study suggests, most individual cancer mutations are due to random chance, the researchers admit that the cancers they cause may still be preventable.

伦敦癌症研究所进化与癌症中心董事梅尔•格里夫斯教授表示：“虽然正如这项研究显示的那样，大多数癌基因变异是因为细胞分裂时随机产生的错误所致，但是，研究人员也承认说，这种癌症或许也能预防。”

"We have good evidence to show that cancer is caused by a complex mix of environmental exposures, inherited risk, and random chance.

“我们有充分证据表明，癌症的发生是环境因素、遗传风险以及细胞分裂时随机产生的错误这三种因素共同所致。”

"And while the genes we inherit from our parents are unreturnable and many chance events are non-negotiable, fortunately for us, exposures are major contributors to our risk of cancer and offer a route to risk reduction or prevention."

“另外，虽然我们无法改变从父母那里遗传的基因，很多偶然事件也无法避免，但是所幸，环境因素是导致我们患上癌症的主要原因，凭这一点，我们也能降低或防范自己罹癌的风险。”