The Role Of Luck In Getting Cancer
罹癌三大原因：基因、環境、運氣
By Denise Grady

It may sound flippant to say that many cases of cancer are caused by bad luck, but that is what two scientists suggested in an article recently published in the journal Science. The bad luck comes in the form of random genetic mistakes, or mutations, that happen when healthy cells divide.
若說許多癌症病例是運氣不佳所致，聽來可能有點輕率，但那正是兩位科學家最近在《科學》（Science）期刊上所發表的一篇論文中提出的見解。這種惡運發生在健康的細胞分裂時，形式是隨機出現的基因失誤，或者稱為突變。

Random mutations may account for two-thirds of the risk of getting many types of cancer, leaving the usual suspects – heredity and environmental factors – to account for only one-third, say the authors, Cristian Tomasetti and Dr. Bert Vogelstein, of Johns Hopkins University School of Medicine in Baltimore, Maryland.
這篇論文的作者是美國馬里蘭州巴爾的摩市約翰霍普金斯大學的教授托馬塞提與沃格斯坦，他們兩位說，對許多種癌症而言，罹患風險可能有三分之二來自於隨機突變，而常見疑似成因－遺傳及環境因素二者，卻只佔了三分之一。

“We do think this is a fundamental mechanism, and this is the first time there’s been a measure of it,” said Dr. Tomasetti, an applied mathematician.
應用數學家托馬塞提博士說：「我們的確認為這是（與致癌有關的）一項基本機制，而且是頭一次有人把運氣所佔比例加以測量。」

Though the researchers suspected that chance had a role, they were surprised at how big it turned out to be. “This was definitely beyond my expectations,” he said. “It’s about double what I would have thought.”
雖然研究人員原本就已推測運氣在其中扮演曾著一定的角色，他們最終結果證明這個角色竟然占了這麼大的比重，還是感到相當意外。托馬塞提博士說：「這絕對超出了我們的預期，大約是我們原本以為比重的兩倍。」

The finding may be good news to some people, bad news to others, he added.
托馬塞提博士接著說，這項發現對某些人來說可能是好消息，對其他人來說則可能是壞消息。

Smoking greatly increases the risk of lung cancer, but for other cancers, the causes are not clear. And yet many patients wonder if they did something to bring the disease on themselves, or if they could have done something to prevent it.
吸菸會大幅增加罹患肺癌的風險，但對其他種類的癌症而言，致癌原因卻並不清楚。然而許多病患都想要知道，他們是否做了什麼事才害自己惹病上身。或者有那些事他們要是做了，就可以不致罹患癌症的。

“For the average cancer patient, I think this is good news,” Dr. Tomasetti said. “Knowing that over all, a lot of it is just bad luck, I think in a sense it’s comforting.”
托馬塞提博士說：「對一般癌症患者而言，我認為這是個好消息。知道大致來說罹患癌症有很大一部分原因只是運氣不好，我認為從某種意義上來說，能夠令人感到寬慰。」

Among people who do not have cancer, Dr. Tomasetti said he expected there to be two camps.
托馬塞提博士說，至於那些沒有罹患癌症的人，他認為可以分成兩派。

“There are those who would like to control every single thing happening in their lives, and for those, this may be very scary,” he said. “ ‘There is a big component of cancer I can just do nothing about.’
他說：「有一種人喜歡控制他們生活中的每一件事，對這些人來說，上述發現可能非常嚇人。『有那麼大的一項癌症成因，是讓我束手無策的。』

“For the other part of the population, it’s actually good news. ‘I’m happy. I can of course do all I know that’s important to not increase my risk of cancer, like a good diet, exercise, avoiding smoking, but on the other side, I don’t want to stress out about every single thing or every action I take in my life, or everything I touch or eat.’ ”
「對另一種人，這真是好消息。『我很高興，我當然可以做所有我知道不會增加罹癌風險的重要事，例如健康攝食、運動、避免吸菸，但在另一方面，我不希望對每件事、我採取的每項行動，或我碰觸、吃進的每件東西感到緊張而崩潰。』」

Dr. Vogelstein said the question of causation had haunted him for decades, since he was an intern and his first patient was a 4-year-old girl with leukemia. Her parents were distraught and wanted to know what had caused the disease.
沃格斯坦說，從他還是實習醫師、第一個病患是個罹患血癌的四歲小女孩起，因果關係這個問題已纏繞他數十年。小女孩的父母心煩意亂，想知道是什麼原因造成血癌。

He had no answer, but time and time again heard the same question from patients and their families, particularly parents of children with cancer.
當時他沒有答案，但他後來從病患和家屬那裡，特別是癌症病童的父母那裡，一再聽到相同的問題。

“They think they passed on a bad gene or gave them the wrong foods or exposed them to paint in the garage,” he said. “And it’s just wrong. It gave them a lot of guilt.”
他說：「家長們認為是自己把不良基因傳給子孩子、給孩子吃了不當的食物，或讓孩子接觸到車庫裡的油漆。那全都錯了，那些原因帶給家長強烈的罪惡感。」

Dr. Tomasetti and Dr. Vogelstein said the finding that so many cases of cancer occur from random genetic accidents means that it may not be possible to prevent them, and that there should be more of an emphasis on developing better tests to find cancers early enough to cure them.
托馬塞提和沃格斯坦說，許多癌症是在隨機出現的基因意外下發生，這項發現意味癌症或許是不可能避免的，而且應該更強調研發較佳的檢驗辦法，以便及早發現、治療。

“Cancer leaves signals of its presence, so we just have to basically get smarter about how to find them,” Dr. Tomasetti said.
托馬塞提說：「癌症出現時會有跡象，因此我們必須變得更聰明，想辦法找出癌症。」

Their conclusion comes from a statistical model they developed using data in the medical literature on rates of cell division in 31 types of tissue. They looked specifically at stem cells, which are a small, specialized population in each organ or tissue that divide to provide replacements for cells that wear out.
他們的結論來自兩人利用31種組織細胞分裂率的醫學文獻資料，研發出一個統計模型。他們特別檢視了幹細胞－每個器官或組織中的一小群專門細胞，會分裂以取代壞死細胞。

Dividing cells must make copies of their DNA, and errors in the process can set off the uncontrolled growth that leads to cancer. The researchers wondered if higher rates of stem-cell division might increase the risk of cancer simply by providing more chances for mistakes.
分裂中的細胞必須複製其DNA，過程中的失誤會啟動無法控制的增生，導致癌症。兩位研究人員懷疑，幹細胞分裂率較高，可能就增加了癌症的風險。

The analysis did not include breast or prostate cancers, because there was not enough data on rates of stem-cell division in those tissues.
這項分析並未納入乳癌或前列腺癌，因為並無乳房及前列腺組織幹細胞分裂率的足夠資料。

A starting point for their research was an observation made more than 100 years ago but never really explained: Some tissues are far more cancer-prone than others. In the large intestine, for instance, the lifetime cancer risk is 4.8 percent – 24 times higher than in the small intestine, where it is 0.2 percent.
他們研究的起點是一項源於100年前但從未真正釐清觀察：有些組織遠比其他組織容易罹癌。例如大腸，終身罹癌風險是4.8%，是小腸罹癌風險0.2%的24倍。

The scientists found that the large intestine has many more stem cells than the small intestine, and that they divide more often: 73 times a year, compared with 24 times. In many other tissues, rates of stem cell division also correlated strongly with cancer risk.
兩位科學家發現，大腸的幹細胞比小腸多，大腸幹細胞一年分裂73次，也比小腸的24次來的頻繁。在許多其他組織中，幹細胞的分裂率也與癌症風險高度相關。

Some cancers, including certain lung and skin cancers, are more common than would be expected just from their rates of stem-cell division – which matches up with the known importance of environmental factors like smoking and sun exposure in those diseases. Others more common than expected were linked to cancer-causing genes.
有些癌症，包括某些肺癌和皮膚癌，比單從織幹細胞分裂率推斷所得者來得普遍，這與吸菸及曝曬之類環境因素在這兩種癌症上已知的重要性相符。其他比預期更普遍的癌症則與致癌基因有關。

Dr. Tomasetti said, “It’s really the combination of inherited factors, environment and chance.”
托馬塞提說：「癌症成因實際上是遺傳因素、環境及運氣的組合。」

原文參照：
http://www.nytimes.com/2015/01/06/health/cancers-random-assault.html

2015-01-20聯合報/G5版/UNITED DAILY NEWS 馮克芸譯 原文參見紐時週報十版左