This page tells you about how a cancer gets
its blood supply. There is information on
How a cancer cell grows
A cancerous tumour is made up of billions of cancer cells. The tumour gets bigger
because the number of cells increases. Each individual cell goes through a
growth cycle again and again, doubling into two cells each time. There is
more about this in our section about cells
and cancer.
As the tumour gets bigger, the centre of it
gets further and further away from the blood vessels in the area where it is
growing. So the centre of the tumour gets less and less of the oxygen and
the other nutrients all cells need to survive.In fact, scientists researching how tumours grow now think that a cancer
can't grow much bigger than a pin head before it has to develop its own
blood supply. Until it does, it will not grow any bigger because cells at
the edge of the tumour will die through lack of oxygen.
Carcinoma in situ
Cancer at this very
early stage is often called 'carcinoma in situ'. This just means that it
hasn't spread into the surrounding area, or spread anywhere else in the
body. Some researchers think that cancers get to this point and may stop
developing for many months or years.
Unfortunately, these cancers are still so small that they will probably not
be found unless they are somewhere where they are easy to spot, for example
in the skin, or on the cervix where they are found during a smear. A
carcinoma in situ in an internal organ will usually be too small to pick up
on a scan. The exceptions are breast cancer and cervical cancer. Carcinomas
in situ can be picked up on mammograms and in cervical smears.Angiogenesis
Normal cells can stimulate new blood vessels to grow. This happens to
repair damaged tissue whenwounds are healing and is called 'angiogenesis'.
So normal cells have genes that can switch blood vessel growth on and off.
The proteins made by these genes are called 'angiogenic factors' and 'antiangiogenic
factors'.
Researchers into angiogenesis
think that this is the big difference between a carcinoma in
situ and a growing cancer. They think that for some time, a carcinoma
in situ may not be able to spread - it is 'dormant'. Then, it may suddenly
begin to be able to trigger the growth of tiny blood vessels called
'capillaries'. The cancer can then begin to grow again and spread to the
body tissues that surround it.
The tumour cells may have mutated and lost
antiangiogenic genes (the 'off switches' for blood vessel growth). Or their
angiogenic genes ('on switches') may have become permanently switched on.
What is most likely is that both these things have happened and it is the
balance between the two that is important. The tumour cells may also be
able to stimulate other normal cells to produce angiogenic factors.
Once a tumour can stimulate the growth of blood vessels, it can grow very
fast. It will stimulate the growth of hundreds of new capillaries from the
nearby blood vessels and these bring it nutrients and oxygen.
Angiogenesis and cancer spread
Scientists also think
angiogenesis may play a part in cancer spread. They have found that the
newly developing capillary cells release substances that help the cancer
cells to detach from the primary tumour and get into the blood stream. This
will mean that the cells can travel to another part of the body and begin to
grow there.
Angiogenesis may also explain why a secondary cancer can appear years after
the primary. Sometimes, cancer cells that have spread may not yet be able
to stimulate the growth of blood vessels. A small secondary could develop,
similar to a carcinoma in situ. The cells continue to multiply and mutate,
but the cancer cannot get much bigger.
Through mutation, the cells may suddenly begin to be able to trigger blood
vessel growth many months or even years later. A secondary cancer would
then begin to grow rapidly and would soon be discovered.
Research
into angiogenesis
A lot of research is going on into
angiogenesis. The research has found that the concentration of these
angiogenic factors is very high at the outer edges of a tumour.
Antiangiogenic drugs may stop a cancer from growing into surrounding tissue
or spreading. They will probably not be able to get rid of a cancer, but
may be able to stabilise the disease in some cases. A number of different
substances that researchers have found to be antiangiogenic are already
being researched. If trials are currently recruiting, they will be listed
on our clinical trials
database. Examples of drugs that interfere with blood vessel growth are
