- [Narrator] Today cancer causes
one in every seven deaths worldwide.
But how does cancer start,
and what is being done to combat it?
Our bodies contain trillions
of highly specialized cells
and each carries genes responsible
for regulating cell growth and division.
But when a genetic change
disrupts this process
cells begin to grow and
divide uncontrollably
thereby becoming cancer.
The genetic changes that cause cancer
usually happen in three types of genes.
Proto-oncogenes, which signal
a cell to grow and divide.
Tumor suppressor genes,
which signal a cell to stop dividing.
And DNA repair genes,
which preserve and maintain genetic codes.
Changes in these genes lead
to abnormal cell growth
resulting in masses of
tissues called tumors.
Tumors may be benign, meaning
that they remain in one area,
or malignant, which means
that they are capable of spreading.
Through a process called metastasis
a malignant tumor's cells
will eventually break off,
travel throughout the body,
and begin forming tumors in other regions.
When this happens the
cancer has become metastatic
and is most dangerous.
The cause of cancer is still a mystery.
Inherited traits may be behind
some of the genetic changes
that lead to the formation
of cancerous cells,
and so might environmental exposures.
Such as excessive radiation from the sun,
or chemicals in cigarette smoke.
In the United States today
roughly one-third of all people
will eventually develop cancer.
Of the over 100 different types of cancer
breast cancer is currently
the most prevalent type,
and lung cancer causes the most deaths.
But our ability to fight
cancer is improving.
Since just the 1990s
cancer mortality rates
have dropped more than 26% in the US,
and more than two million
lives have been saved.
As treatments and methods
of early detection improve,
and doctors, scientists, and the public
better understand cancer,
hope remains in the fight
against the disease.
