body normally controls this process. In
some people, however, certain cells start
to multiply too much. These cells are
not normal. They produce clumps of
tissue called tumors.
Some tumors are harmless, but others
are very serious. They can destroy
nearby healthy cells and organs. These
destructive tumors are called cancer.
Cells from these tumors sometimes
spread to other parts of the body and
form more tumors.
There are many different kinds of cancer.
The kind of cancer a person has
depends on where it starts to grow. It
also depends on what causes it and how
fast it grows.
Symptoms
There are some general symptoms, or
signs, that may mean a person has cancer.
These symptoms include pain,
weight loss that cannot be explained,
fever, tiredness, and changes in the skin.
Each kind of cancer also produces specific
symptoms. For example, a cough
that will not go away could be a sign of
lung cancer.
Causes
Scientists do not know why some cells
multiply too quickly. However, they
have discovered many things that can
lead to cancer. Most cancers are caused
by conditions outside the body. For
example, getting too much sunlight can
cause skin cancer. Smoking tobacco can
cause lung or mouth cancer.
As a tumor grows larger, it invades the
healthy tissues nearby. Cancer spreads when
cells from a tumor travel to other parts of the
body.
30 Cancer BRITANNICA STUDENT ENCYCLOPEDIA
In addition, eating unhealthy foods and
not exercising enough can lead to cancer.
People have a higher chance of getting
some kinds of cancer if members of
their families had them. A few viruses
also cause cancer.
Prevention
The easiest way to prevent cancer is to
stay away from the things that might
cause it. For example, doctors suggest
that people wear sunscreen lotion when
outdoors. Sunscreen lotion protects the
skin from harmful rays in sunlight.
Exercise and eating a lot of fruits, vegetables,
and whole grains also can help
to prevent cancer. Seeing a doctor once a
year helps, too. Doctors can find early
warning signs of cancer.
Treatment
If cancer is caught early, it often can be
treated successfully. A doctor can remove
tumors by surgery, or cutting them out
of the body. Radiation (energy particles)
and chemotherapy (chemicals) are also
used in cancer treatment. These two
processes either kill the cancer cells or
stop them from growing.
#More to explore
Cell • Disease, Human
Canyon
A canyon is a narrow, deep valley cut
by a river through rock. Canyons vary
in size. Some are narrow slits while
others are huge trenches. Canyons have
very steep sides and may be thousands
of feet deep. Smaller valleys of similar
appearance are called gorges.
Canyons are created by erosion. Over
thousands or millions of years a river’s
flowing water erodes, or wears away, soil
and rocks to form a valley. The largest
and most famous canyons have been cut
through dry areas by swift streams fed by
rain or melting snow from wetter areas.
The walls remain steep and rough
because there is little rainfall or surface
water to wear them down. An example is
the Grand Canyon, in the U.S. state of
Arizona.
Submarine canyons are deep underwater
valleys. They are found along the borders
of the continents and some ocean
islands. The Grand Bahama Canyon, in
the Atlantic Ocean near the Bahamas, is
thought to be the deepest submarine
Over many years, Deer Creek
has cut through rock to create a
beautiful canyon in Grand Canyon
National Park, Arizona.
BRITANNICA STUDENT ENCYCLOPEDIA Canyon 31
canyon. Its walls are nearly 3 miles (5
kilometers) tall.
..More to explore
Continent • Erosion • Grand Canyon
• River
Cape Town
Population
(2005 estimate)
3,103,000
The country of South Africa has three
capitals—Cape Town, Pretoria (Tshwane),
and Bloemfontein. Cape Town is
where the country’s legislature meets.
The legislature makes the country’s laws.
It is a large city in a beautiful natural setting.
Cape Town is one of South Africa’s most
important centers of industry. Factories
in the city process foods and make wine,
clothing, and leather goods. Other main
industries include ship repair and tourism.
Cape Town is also a seaport.
The first people to live in the region
were ancestors of the African Khoisan
people. Traders from the Netherlands
founded a settlement at the site in 1652.
It was the first European settlement in
what is now South Africa. The company
used the settlement as a supply station.
In 1806 the British took control of the
area. In the late 1800s the discovery of
gold and diamonds nearby brought
many more people to Cape Town. In
1910 the country of South Africa was
formed with Cape Town as its legislative
capital.
..More to explore
Bloemfontein • Pretoria • South Africa
The city of Cape Town, South Africa, looks
out onto the Atlantic Ocean.
Plants grow on the walls and
floor of a canyon in Iceland.
Many famous canyons are found
in dry regions, but canyons also
may form in cool, wet areas.
32 Cape Town BRITANNICA STUDENT ENCYCLOPEDIA
Cape Verde
Cape Verde is an archipelago, or group
of islands, in the Atlantic Ocean. Ruled
by Portugal for 500 years, the country
gained independence in 1975. Praia, on
