This year, 50 percent of the 910,000 people who suffer from cancer will survive ai least fiveyears. In the year 2000. the National Cancer Institute estimates, that figure will be 75 percent.For some skin cancers, the five-year survival rate is as high as 90 percent. But other survivalstatistics are still discouraging-13 percent for lung cancer. and 2 percent for cancer of thepancreas(胰腺)。

　　With as many as 120 varieties in existence, discovering how cancer works is not easy. Theresearchers madegreat progress in the early 1970s. when they discovered that oncogenes.which are cancer-causing genes (基因), are inactive in normal cells. Anything from cosmic raysto radiation to diet may activate a dormant oncogene. but how remains unknown. If severaloncogenes are driven into action the cell. unable to turn them off. becomes cancerous.

　　The exact mechanisms involved are still mysterious, but the likelihood that many cancers areinitiated ai the level of genes suggests that we will never prevent all cancers. "Changes are anormal pan of the evolutionary process." says oncologist William Hayward. Environmentalfactors can never be totally eliminated; as Hayward points out, "We can't prepare a medicineagainst cosmic rays. "

　　The prospects for cure.though still distant, are brighter.

　　"First we need io understand how the normal cell controls itself. Second,we have todetermine whether there are a limited number of genes in cells which are always responsiblefor al least pan of the trouble. If we can understand how cancer works. we can counteract itsaction."

　　“我很有把握，到本年代末，我們會非常詳細地了解到癌細胞是如何產生的，”癌癥專家、微生物學家羅伯特·溫伯格說。[1]“但是，”他警告說，“有些人認為，一旦有人找到了病因，治療方法馬上就隨之而來了。想想巴斯德吧!他發現了許多種感染的原因，但是五六十年后才找到治療方法。”

　　今年，患癌癥的91萬人中，有50%至少可以活5年。國家癌癥研究所估計，到2000年，這個比例將上升到75%。在患某些皮膚癌的人中，5年存活率高達90%。但是其他癌癥患者中能活5年的人所占比例仍令人沮喪——肺癌為13%，胰腺癌為2%。

　　[2]因為已發現的癌癥種類多達l20種，要找出癌癥是如何發生的并不容易。20世紀70年代初，研究人員取得了重大進展。他們發現，致癌基因——誘發癌癥的基因——在正常細胞中不活躍。任何因素，包括宇宙射線、輻射、飲食，都可能激活不活躍的致癌基因。但激活的機制尚無人知曉。[3]如果幾個致癌基因被激活，細胞無法將其阻斷，就發生癌變。

　　其中確切的機制仍是一個謎，但一種可能性是，許多種癌癥是從基因層次開始的，這說明，我們將永遠無法防止所有的癌癥發生。“進化過程中發生變化是很正常的事，”腫瘤學家威廉·海沃德說。[4]環境因素永遠也無法徹底消除;正如海沃德指出的，“我們無法制出藥物來防止宇宙射線。”

　　治療方法前景雖然還很渺茫，但畢竟樂觀一些了。

　　“首先，我們必須弄清楚，正常細胞如何自我控制。其次，我們得確定，是不是至少有部分麻煩總是由細胞中數量不多的一些基因所致。[5]如果我們能弄清楚癌癥是如何起作用的，我們就可以抑制其活動。”

　　1.Robert Weinberg warns that the discovery of the causes or cancer cells won't necessarily leadto_______________________.

　　2.It is not easy to rind out how cancer works because__________________.

　　3.Once oncogenes in cells are at work.the cell will become_______________________.

　　4.By saying "We can't prepare a medicine against cosmic rays", William Hayward implies that itis impossible to avoid che impact of_______________________.

　　5.Provided that the mechanisms of cancer are found out we are ableto_______________________.

　　1.[the rapid discovery of its cure]