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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.