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Why is it so difficult to cure cancer?
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We've harnessed electricity,
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sequenced the human genome,
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and eradicated small pox.
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But after billions of dollars in research,
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we haven't found a solution for a disease that affects more than 14 million people
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and their families at any given time.
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Cancer arises as normal cells accumulate mutations.
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Most of the time, cells can detect mutations or DNA damage
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and either fix them or self destruct.
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However, some mutations allow cancerous cells to grow unchecked
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and invade nearby tissues,
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or even metastasize to distant organs.
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Cancers become almost incurable once they metastasize.
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And cancer is incredibly complex.
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It's not just one disease.
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There are more than 100 different types
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and we don't have a magic bullet that can cure all of them.
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For most cancers,
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treatments usually include a combination of surgery to remove tumors
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and radiation and chemotherapy to kill any cancerous cells left behind.
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Hormone therapies,
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immunotherapy,
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and targeted treatments tailored for a specific type of cancer
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are sometimes used, too.
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In many cases, these treatments are effective
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and the patient becomes cancer-free.
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But they're very far from 100% effective 100% of the time.
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So what would we have to do to find cures for all the different forms of cancer?
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We're beginning to understand a few of the problems
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scientists would have to solve.
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First of all, we need new, better ways of studying cancer.
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Most cancer treatments are developed using cell lines grown in labs
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from cultures of human tumors.
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These cultured cells have given us critical insights
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about cancer genetics and biology,
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but they lack much of the complexity of a tumor in an actual living organism.
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It's frequently the case that new drugs, which work on these lab-grown cells,
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will fail in clinical trials with real patients.
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One of the complexities of aggressive tumors
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is that they can have multiple populations of slightly different cancerous cells.
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Over time, distinct genetic mutations accumulate in cells
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in different parts of the tumor, giving rise to unique subclones.
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For example, aggressive brain tumors called glioblastomas
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can have as many as six different subclones in a single patient.
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This is called clonal heterogeneity,
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and it makes treatment difficult because a drug that works on one subclone
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may have no effect on another.
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Here's another challenge.
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A tumor is a dynamic interconnected ecosystem
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where cancer cells constantly communicate with each other
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and with healthy cells nearby.
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They can induce normal cells to form blood vessels that feed the tumor
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and remove waste products.
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They can also interact with the immune system
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to actually suppress its function,
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keeping it from recognizing or destroying the cancer.
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If we could learn how to shut down these lines of communication,
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we'd have a better shot at vanquishing a tumor permanently.
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Additionally, mounting evidence suggests
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we'll need to figure out how to eradicate cancer stem cells.
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These are rare but seem to have special properties
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that make them resistant to chemotherapy and radiation.
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In theory, even if the rest of the tumor shrinks beyond detection during treatment,
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a single residual cancer stem cell could seed the growth of a new tumor.
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Figuring out how to target these stubborn cells
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might help prevent cancers from coming back.
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Even if we solved those problems, we might face new ones.
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Cancer cells are masters of adaptation,
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adjusting their molecular and cellular characteristics to survive under stress.
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When they're bombarded by radiation or chemotherapy,
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some cancer cells can effectively switch on protective shields
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against whatever's attacking them by changing their gene expression.
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Malignant cancers are complex systems that constantly evolve and adapt.
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To defeat them, we need to find experimental systems
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that match their complexity,
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and monitoring and treatment options that can adjust as the cancer changes.
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But the good news is we're making progress.
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Even with all we don't know,
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the average mortality rate for most kinds of cancer
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has dropped significantly since the 1970s and is still falling.
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We're learning more every day,
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and each new piece of information gives us one more tool to add to our arsenal.
