C a n c e r     A w a r e n e s s Introduction Part 3
15 June 2015

Metastasis:

The main reason cancer can be difficult to cure is that it can spread to a different part of the body from where it started.
The cancer that grows where it first started in the body is called the 'primary cancer'. The place a cancer spreads to and
then starts growing are called the 'secondary cancer' or 'metastasis'.

In order to spread, some cells from the primary cancer must break away, travel to another part of the body and start growing
there. Cancer cells do not stick together as well as normal cells do. They also may produce substances that stimulate them
to move.

There are three main ways a cancer spreads
•Local spread
•Through the blood circulation
•Through the lymphatic system

Local spread

As a tumour gets bigger, it takes up more and more room in the body. Soon it begins to grow into the body structures nearby.
This is called local invasion. How a cancer actually grows into surrounding normal body tissues is not fully understood. But
research has pointed to 3 ways that the tumour is most likely to do this

•Pressure from the growing tumour
•Using enzymes
•Cancer cell moving through the tissue

A particular tumour will probably use all 3 of these ways of spreading. Which way is used most will depend partly on the type of
tumour, and partly on where in the body it is growing.

As the tumour grows and takes up more space, it begins to press on the normal body tissue nearby. The tumour growth will force
itself through the normal tissue, as in the diagram below.

The finger like appearance of the growth happens because it is easier for the growing cancer to force its way through some paths
than others - for example, cancers may grow between sheets of muscle tissue rather than straight through one particular sheet.
As the cancer grows, it will squeeze and block small blood vessels in the area. Due to low blood and oxygen levels, some of the
normal tissue will begin to die off. This makes it easier for the cancer to continue to push its way through.

Many normal blood cells produce chemicals called enzymes that break down cells and tissues. The blood cells use their enzymes to
attack invading bacteria and viruses. They also use them to break down and clear up damaged areas in the body. The damaged cells
have to be cleared away so that the body can replace them with new ones. This is all part of the natural healing process.

Many cancers contain larger amounts of these enzymes than normal tissues. Some cancers also contain a lot of normal white blood
cells. They are part of the body's immune response to the cancer. We're not yet sure where the enzymes come from, but they are
likely to make it easier for the cancer to make a pathway for itself through the healthy tissue.

One of the things that make cancer cells different to normal cells is that they can move about more easily. So it seems likely that
one of the ways that cancers spread through nearby tissues is by the cells directly moving. Scientists have discovered a substance made
by cancer cells which stimulates them to move. They don't know for sure yet, but it seems likely that this substance plays a big part in
the local spread of cancers.

A cancer probably just grows out in a random direction from the place where it started. However, tumours can spread into some tissues
more easily than others. For example, large blood vessels that have very strong walls and dense tissues such as cartilage are hard for
tumours to grow into. So locally, tumours grow along the 'path of least resistance'. This means that they probably just take the easiest
route.

Through the blood circulation

Blood carries nutrients (food) and oxygen to all the cells of the body, and carries away waste products so that they can be removed
from the body.Without a blood supply, cells and body tissues die.

The blood moves around the body inside the circulatory system. This is made up of blood vessels (tubes) called arteries, veins and
capillaries.The blood keeps moving through these blood vessels because it is pumped by the heart.

Arteries carry blood that is full of oxygen from the heart to all parts of the body. As the arteries get further and further
away from the heart,they get smaller and smaller. Eventually they turn into capillaries. These are the smallest blood vessels.
They go right into the tissues. Here the blood in the capillaries gives oxygen to the cells and picks up the waste gas, carbon
dioxide, from the cells.

The capillaries are connected to the smallest veins in the body. The veins get bigger and bigger as they carry the blood
back towards the heart. The blood passes through the right side of the heart and goes to the lungs where it gets rid of
carbon dioxide and picks up more oxygen. It then passes through the left side of the heart and is pumped back around the body.

The blood always circulates through the body in the same direction. As well as oxygen and carbon dioxide, many other substances
are carried in the blood. The blood circulating through the digestive system picks up digested food products and carries them to
the liver to be used or stored.

The circulation can help explain why some cancers nearly always spread to the same place. Cancers of the colon (large bowel)
often spread to the liver. This is because blood circulates from the bowel through the liver on its way back to the heart.
If there is a cancer in the large bowel, and some cancer cells escape into the circulation, they may stick in the liver as the
blood passes through. They can then begin to grow into secondary cancers.

Although blood looks like a red liquid, if left in a test tube it separates out into pale liquid called plasma and a
solid layer of blood cells

The blood is about 55% plasma and 45% cells. Plasma is mostly water with some proteins and other chemicals dissolved in it.
There are three main types of cells in the blood
•White blood cells
•Red blood cells
•Platelets

In order to spread, the cancer cell must first become detached from the primary cancer. It must then move through the wall
of a blood vessel to get into the bloodstream.

When it is in the bloodstream, it is swept along by the circulating blood until it gets stuck somewhere, usually in a very
small blood vessel called a capillary. Then it must move back through the wall of the capillary and into the tissue of the
organ close by. There it must start to multiply to grow a new tumour.

This is a complicated journey. Most cancer cells do not survive it. Probably, out of many thousands of cancer cells that
reach the blood circulation only one will survive to form a secondary cancer or metastasis.

Some cancer cells are probably killed off by the white blood cells in our immune system. Others cancer cells may die
because they are battered around by the fast flowing blood.

Cancer cells in the circulation may try to stick to platelets to form clumps to give themselves some protection. This may
also help them to be filtered out in the next capillary network they come across so they can then move into the tissues to start
a secondary tumour.

Through the lymphatic system

The way a cancer spreads through the lymphatic system is very similar to the way it spreads through the bloodstream. The
cancer cell must become detached from the primary tumour. Then it travels in the circulating lymph fluid until it gets stuck
in the small channels inside a lymph node. There it begins to grow into a secondary cancer.

The lymphatic system is a system of thin tubes that runs throughout the body. These tubes are called lymph vessels or lymphatic
vessels.

The lymphatic system is like the blood circulation - the tubes (vessels) branch through all parts of the body like the
arteries and veins that carry blood. But the lymphatic system tubes are much finer and carry colourless liquid called lymph.

Lymph is a clear fluid that circulates around the body tissues. It contains a high number of lymphocytes.

Plasma leaks out of the capillaries to surround and bathe the body tissues. This then drains into the lymph vessels.

The fluid, now called lymph, then flows through the lymphatic system to the biggest lymph vessel - the thoracic duct. The
thoracic duct thenempties back into the blood circulation.

Along the lymph vessels are small bean-shaped lymph glands or 'nodes'.

We can probably feel some of our lymph nodes. There are lymph nodes in many parts of our body including
•Under our arms, in our armpits
•In each groin (at the top of our legs)
•In our neck

There are also lymph nodes that we cannot feel in
•our abdomen
•our pelvis
•our chest

Other lymphatic system organs
The lymphatic system includes other body organs. These are the
•Spleen
•Thymus
•Tonsils
•Adenoids

The spleen is under our ribs on the left side of our body. The spleen has two main different types of tissue,
red pulp and white pulp. The red pulp filters worn out and damaged red blood cells from the blood and recycles them.
The white pulp contains many B lymphocytes and T lymphocytes. These are white blood cells that are very important for
fighting infection. As blood passes through the spleen, these blood cells pick up on any sign of infection and begin
to fight it. The thymus is a small gland under our breast bone. The thymus helps to produce white blood cells. It is
usually most active in teenagers and shrinks in adulthood.

The tonsils are two glands in the back of your throat. The adenoids are at the back of your nose, where it meets the
back of your throat. The tonsils and adenoids (also called the 'nasopharyngeal' tonsils) help to protect the entrance to
the digestive system and the lungs from bacteria and viruses.

The lymphatic system does several jobs in the body. It
•Drains fluid back into the bloodstream from the tissues
•Filters lymph
•Filters the blood
•Fight infections

As the blood circulates, fluid leaks out from the blood vessels into the body tissues. This fluid is important because it
carries food to the cells and waste products back to the bloodstream. The leaked fluid drains into the lymph vessels. It is
carried through the lymph vessels to the base of the neck where it is emptied back into the bloodstream. This circulation of
fluid through the body goes on all the time.

The lymph nodes filter the lymph fluid as it passes through. White blood cells attack any bacteria or viruses they find in the
lymph as it flows through the lymph nodes. If cancer cells break away from a tumour, they often become stuck in the nearest lymph
nodes. This is why doctors check the lymph nodes first when they are working out how far a cancer has grown or spread.

This is the job of the spleen. It filters the blood to take out all the old worn out red blood cells and then destroys them.
They are replaced by new red blood cells that are made in the bone marrow. The spleen also filters out bacteria, viruses and
other foreign particles found in the blood.
White blood cells in the spleen attack bacteria and viruses as they pass through.

When people say "I'm not well, my glands are up" they are really saying they have swollen lymph nodes because they have an infection. The lymphatic system helps fight infection in many ways such as
•Helping to make special white blood cells (lymphocytes) that produce antibodies
•Having other blood cells called macrophages inside the lymph nodes which swallow up and kill any foreign particles,
for example germs This function of the lymphatic system is really part of the immune system.