Why is it so difficult to cure cancer?
为什么治愈癌症如此困难？
We've harnessed electricity, sequenced the human genome, and eradicated small pox.
我们已经成功开发了电力，给人类基因组进行了排序，成功根治了水痘。
But after billions of dollars in research,
但是在科学研究上花费了数十亿美元后，
we haven't found a solution for a disease that affects more than 14 million people and their families at any given time.
我们还是没办法治愈一种影响着超过1400万人和家庭的疾病。
Cancer arises as normal cells accumulate mutations.
癌症的病因是正常细胞的变异增多。
Most of the time, cells can detect mutations or DNA damage and either fix them or self destruct.
大多数时候，细胞可以检测到变异或DNA受损，然后进行修复或者自我毁灭。
However, some mutations allow cancerous cells to grow unchecked and invade nearby tissues, or even metastasize to distant organs.
然而，有些变异会让癌变的细胞悄悄增长，然后侵入附近的组织，或者转移到其它的器官。
Cancers become almost incurable once they metastasize.
癌变细胞一旦转移就无法医治。
And cancer is incredibly complex. It's not just one disease.
而且癌症非常复杂，它并不是单一的疾病。
There are more than 100 different types and we don't have a magic bullet that can cure all of them.
癌症有100多个种类，我们还没有一个能治愈所有癌症的万能药。
For most cancers, treatments usually include a combination of surgery to remove tumors
就大多数癌症来讲，治疗方式通常包括动手术切除肿瘤、
and radiation and chemotherapy to kill any cancerous cells left behind.
做放射及化疗来除掉剩余的癌细胞。
Hormone therapies, immunotherapy, and targeted treatments tailored for a specific type of cancer are sometimes used, too.
激素疗法，免疫治疗和针对某种癌症的定制疗法有时候也会被采用。
In many cases, these treatments are effective and the patient becomes cancer-free.
很多情况下，这些治疗方式很有效，病人可以被治愈。
But they're very far from 100% effective 100% of the time.
但是这些疗法绝不算是百分百的成功。
So what would we have to do to find cures for all the different forms of cancer?
那我们该怎样找到治愈不同种癌症的解决方案呢？
We're beginning to understand a few of the problems scientists would have to solve.
目前我们已经开始明白科学家们该向哪些方向努力了。
First of all, we need new, better ways of studying cancer.
首先，我们需要更新和更好的研究癌症的方法。
Most cancer treatments are developed using cell lines grown in labs from cultures of human tumors.
大多数癌症治疗法都是使用实验室培育的细胞研发出来的，这些细胞来自人类的肿瘤体。
These cultured cells have given us critical insights about cancer genetics and biology,
这些实验室培育的细胞对于我们理解癌症基因和生物机理来说非常关键，
but they lack much of the complexity of a tumor in an actual living organism.
但这种细胞缺失了活体内肿瘤所含有的复杂性。
It's frequently the case that new drugs, which work on these lab-grown cells, will fail in clinical trials with real patients.
通常，新研发出的药在实验室细胞上药效不错，但是试用在真正的病人身上却没效果。
One of the complexities of aggressive tumors is that they can have multiple populations of slightly different cancerous cells.
活跃肿瘤的其中一个复杂性在于，即使有些癌细胞间的区别很小，它们也可以产生出多个群体。
Over time, distinct genetic mutations accumulate in cells in different parts of the tumor, giving rise to unique subclones.
时间一长，不同的基因变异在细胞内积累起来，出现在肿瘤的不同部位，产生独特的亚克隆体。

For example, aggressive brain tumors called glioblastomas can have as many as six different subclones in a single patient.
比如，活跃的脑瘤被称为胶质母细胞瘤，在一个母体中可以有多达6个不同的亚克隆体。
This is called clonal heterogeneity,
这种现象叫做克隆异质性。
and it makes treatment difficult because a drug that works on one subclone may have no effect on another.
此特性让治疗变得很困难，能治一种亚克隆体的药可能对另一种完全无效。
Here's another challenge.
我们还面临着一个挑战。
A tumor is a dynamic interconnected ecosystem where cancer cells constantly communicate with each other and with healthy cells nearby.
肿瘤是活跃的相互联系的生态系统，癌细胞们一直在互相交流，也和附近健康的细胞保持着联系。
They can induce normal cells to form blood vessels that feed the tumor and remove waste products.
它们促使正常的细胞形成为癌细胞供应养分和清理废物的血管。
They can also interact with the immune system to actually suppress its function, keeping it from recognizing or destroying the cancer.
它们也可以和免疫系统互动，从而影响系统的正常运作，让其无法识别和摧毁癌变部位。
If we could learn how to shut down these lines of communication, we'd have a better shot at vanquishing a tumor permanently.
如果我们能研究出如何制止这些互动和交流，就有可能永久地消灭癌变。
Additionally, mounting evidence suggests we'll need to figure out how to eradicate cancer stem cells.
另外，越来越多的证据显示，我们需要研究出消除癌症干细胞的方法。
These are rare but seem to have special properties that make them resistant to chemotherapy and radiation.
干细胞不常见，但是它们的特质是对化疗和放射疗法有抵抗性。
In theory, even if the rest of the tumor shrinks beyond detection during treatment,
理论上来讲，即使大多数肿瘤在治疗期间收缩到无法被识别，
a single residual cancer stem cell could seed the growth of a new tumor.
一小点剩余的癌细胞也有可能长成新肿瘤。
Figuring out how to target these stubborn cells might help prevent cancers from coming back.
找到攻克这些倔强细胞的方法也许可以帮助防止癌细胞的复发。
Even if we solved those problems, we might face new ones.
即使我们解决了这些问题，也可能面临新的问题。
Cancer cells are masters of adaptation, adjusting their molecular and cellular characteristics to survive under stress.
癌细胞的适应性非常强，在苛刻的环境下也能通过调整它们的分子和细胞特征生存下来。
When they're bombarded by radiation or chemotherapy,
当它们被放疗和化疗攻击的时候，
some cancer cells can effectively switch on protective shields against whatever's attacking them by changing their gene expression.
有些癌细胞可以有效转换到自卫模式，改变它们的基因特征，抵抗向它们发起进攻的因素。
Malignant cancers are complex systems that constantly evolve and adapt.
恶性癌症有着复杂的系统，适应性强，变化多端。
To defeat them, we need to find experimental systems that match their complexity,
要想攻克恶性癌症，我们需要找到和它们有相似复杂性的实验系统，
and monitoring and treatment options that can adjust as the cancer changes.
以及随着癌细胞的变化而调整的监测和治疗方案。
But the good news is we're making progress.
值得欣慰的是，我已经取得了进步。
Even with all we don't know,
即使我们目前对癌症的了解还不够多，
the average mortality rate for most kinds of cancer has dropped significantly since the 1970s and is still falling.
但大多数种类癌症的平均致死率已经从20世纪70年代开始大幅度持续降低。
We're learning more every day, and each new piece of information gives us one more tool to add to our arsenal.
我们每天都有新的研究成果，每一点科研的新进展都使我们抗击癌症的军火库更加壮大。