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During World War I, one of the horrors of trench warfare
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was a poisonous yellow cloud called mustard gas.
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For those unlucky enough to be exposed,
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it made the air impossible to breathe, burned their eyes,
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and caused huge blisters on exposed skin.
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Scientists tried desperately to develop an antidote to this vicious weapon of war.
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In the process they discovered the gas was irrevocably damaging the bone marrow
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of affected soldiers— halting its ability to make blood cells.
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Despite these awful effects, it gave scientists an idea.
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Cancer cells share a characteristic with bone marrow: both replicate rapidly.
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So could one of the atrocities of war
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become a champion in the fight against cancer?
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Researchers in the 1930s investigated this idea
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by injecting compounds derived from mustard gas
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into the veins of cancer patients.
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It took time and trial and error to find treatments that did more good than harm,
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but by the end of World War II,
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they discovered what became known as the first chemotherapy drugs.
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Today, there are more than 100.
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Chemotherapy drugs are delivered through pills and injections
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and use "cytotoxic agents," which means compounds that are toxic to living cells.
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Essentially, these medicines cause some level of harm to all cells in the body—
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even healthy ones.
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But they reserve their most powerful effects for rapidly-dividing cells,
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which is precisely the hallmark of cancer.
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Take, for example, those first chemotherapy drugs,
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which are still used today and are called alkylating agents.
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They're injected into the bloodstream,
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which delivers them to cells all over the body.
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Once inside, when the cell exposes its DNA in order to copy it,
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they damage the building blocks of DNA's double helix structure,
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which can lead to cell death unless the damage is repaired.
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Because cancer cells multiply rapidly,
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they take in a high concentration of alkylating agents,
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and their DNA is frequently exposed and rarely repaired.
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So they die off more often than most other cells,
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which have time to fix damaged DNA
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and don't accumulate the same concentrations of alkylating agents.
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Another form of chemotherapy involves compounds called microtubule stabilizers.
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Cells have small tubes that assemble to help with cell division
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and DNA replication, then break back down.
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When microtubule stabilizers get inside a cell,
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they keep those tiny tubes from disassembling.
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That prevents the cell from completing its replication, leading to its death.
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These are just two examples of the six classes of chemotherapy drugs
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we use to treat cancer today.
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But despite its huge benefits, chemotherapy has one big disadvantage:
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it affects other healthy cells in the body that naturally have to renew rapidly.
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Hair follicles, the cells of the mouth, the gastrointestinal lining,
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the reproductive system, and bone marrow are hit nearly as hard as cancer.
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Similar to cancer cells, the rapid production of these normal cells
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means that they're reaching for resources more frequently—
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and are therefore more exposed to the effects of chemo drugs.
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That leads to several common side effects of chemotherapy,
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including hair loss, fatigue, infertility, nausea, and vomiting.
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Doctors commonly prescribe options to help manage these side-effects,
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such as strong anti-nausea medications.
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For hair loss, devices called cold caps can help lower the temperature
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around the head and constrict blood vessels,
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limiting the amount of chemotherapy drugs that reach hair follicles.
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And once a course of chemo treatment is over,
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the healthy tissues that've been badly affected by the drug will recover
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and begin to renew as usual.
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In 2018 alone, over 17 million people world-wide received a cancer diagnosis.
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But chemotherapy and other treatments have changed the outlook for so many.
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Just take the fact that up to 95% of individuals with testicular cancer
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survive it, thanks to advances in treatment.
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Even in people with acute myeloid leukemia— an aggressive blood cancer—
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chemotherapy puts an estimated 60% of patients under 60
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into remission following their first phase of treatment.
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Researchers are still developing more precise interventions
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that only target the intended cancer cells.
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That'll help improve survival rates while leaving healthy tissues
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with reduced harm,
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making one of the best tools we have in the fight against cancer even better.