What is cancer?
Cells normally grow and divide by mitosis
when the body needs new cells to replace old or damaged cells.
Cancer is caused by some genetic fault or change e.g. caused by a
mutation, that leads to uncontrolled growth by cell division
- these are known as cancerous cells and the body does NOT need
them!
The extra mass of cancerous cells formed is called a tumour.
Most tumours are solid, but cancers of the
blood like leukaemia are obviously not.
Tumours can be benign (non-cancerous) and not
usually dangerous, or malignant (cancerous) which are
potentially very harmful.
Benign tumours grow slowly and fill the space available.
A
benign tumour stays in one place e.g. in a membrane and often has a
capsule around it making it quite easy to remove surgically.
Benign tumours are not cancerous and the
cancer cells do not
invade other tissues of the body.
Because they are not cancerous, benign tumours are not usually harmful or dangerous to the body
- but may be removed to stop the cancer from becoming malignant.
Malignant
tumors keep growing faster
then benign tumours, and spread to neighbouring
healthy tissue.
Malignant cells can break away and spread to other
parts of the body in the bloodstream.
* The same malignant cells can
then invade healthy tissue and form secondary tumours in other parts
of the body.
Therefore malignant tumours are highly dangerous
forming potentially fatal cancers.
* As the malignant cells replicate
they can invade surrounding tissue. Unfortunately, this
malignant tumour can secrete hormone-like chemicals that
stimulate blood vessels to grow around the tumour and supply
it with food and oxygen so the cancerous cells further
increase in number. Malignant cells can detach from the
tumour and be transported away in the bloodstream. These
malignant cells can 'squeeze' through a capillary wall and
produce a secondary tumour in a different tissue.
For more on cell division see
Cell division - cell cycle - mitosis, meiosis, sexual/asexual reproduction,
binary fission and cancer
Risk
factors associated with types of cancer
A large proportion of our ever increasing aging
population will eventually suffer from cancer.
300 000 people are diagnosed with cancer in the UK
every year, but it is estimated that 4 in 10 cases are preventable by
making suitable lifestyle choices, and the earlier these choices are
made the better!
We can get a cancer at any stage in our life,
though as we get older our defensive immune system does decline in
response to threats.
Cancer survival rates are continually increasing,
particularly in richer developed countries with their comprehensive
health care services, including early diagnosis from screening
programmes and improved anti-cancer treatments.
Carcinogens
A
carcinogen
is defined as a chemical substance or other agent capable of causing
cancer in living tissue - usually a chemical that promotes changes
in the structure and working of cell DNA.
e.g.
chemicals
in the home, industry or in the environment,
ionising radiation
e.g. from radioactive materials,
lifestyle choices
e.g. alcohol drinking or poor diet,
ultraviolet radiation
from over exposure to sunlight,
viruses
like HPV. More on these in the following notes.
A carcinogen causes cancer by damaging the DNA - that is causing a
mutation
in one or more of the chromosomes in the cells genome,
Mutations can occur by chance as cells are dividing, though most of
these are not damaging because genetic errors are checked for in the
cell cycle and
repairs put in place!
Generally speaking you need several mutations to cause cancer cells
to develop, which is why we become more susceptible to cancer as we
get older - the repair systems become less effective!
Industrial practice and bad lifestyle
habits have been responsible for some of the more common cancers
in the past, particularly in men, but now we know more about the
causes, things are improving for future generations e.g.
Sheets of the mineral asbestos were
widely used in housing and factories for thermal insulation.
Unfortunately, very fine asbestos fibres build up in the air
passages of lungs.
All forms of asbestos increase the risk of lung disease. The
three types of asbestos-related lung disease are scarring (asbestosis),
non-cancerous
disease of the tissue of the lining of the surface of the lung
(pleural disease), and lung cancer (of the lungs or their outer
lining tissue -
mesothelioma).
Several molecules in tobacco tar
are carcinogenic, which you breathe down into your lungs when
smoking.
Genetics - inheritance and mutations
Unfortunately, you can inherit faulty genes
that make a person more susceptible to cancer.
Mutations in the BRCA
genes have been linked to increased chance of women developing
breast cancer or ovarian cancer - a good reason and argument for
cancer screening programmes e.g. cervical smear test for cervical
cancer or x-ray screening for breast cancer.
Ionising radiation - a powerful
carcinogenic agent
Exposure to ionizing radiation - uv, x-ray or
gamma radiations, causes cell damage leading to cancer.
Ionising radiation is therefore described as
carcinogenic.
Diet factors
Obesity - being overweight, is now being
linked to cancers of the bowel, kidney and liver.
Too much fat and sugar in you diet is not
good for your, excess calories the body doesn't need are
converted into fat tissue.
Apparently, statistically, it is the 2nd
biggest preventable cause of cancer, the 1st is smoking!
Osteoporosis
Osteoporosis a medical
condition in which the bones become brittle and fragile from
loss of tissue, typically as a result of hormonal changes, or
deficiency of calcium or vitamin D in your diet.
Meat
Too much red meat and processed meat in
you diet is linked to an increase risk of bowel cancer.
Regular aerobic exercise can
reduce your risk from some non-communicable diseases.
See the
Keeping healthy - diet and exercise
and
Respiration - aerobic and anaerobic in animals
Smoking
- chemicals in tobacco
smoke are carcinogenic.
Giving up smoking, is a lifestyle choice
to reduce your chance of developing lung cancer.
Statistically, stopping smoking is the biggest
preventable cause of cancer.
There is clear evidence of a link between
smoking and contracting lung cancer.
(Its a 'no-brainer' for me, and admit to
smoking cheap nasty cigarettes from the age of 11 to 27!).
However, that's not the only cancer risk from
smoking - it is being linked cancers in the cervix, bowel, mouth and
stomach.
Ultraviolet light (uv) is a powerful
carcinogenic agent.
The more uv light you are exposed too,
including bright sunlight, the greater the chance developing skin
cancer - uv damages skin cells including burns or causing mutations
in the skin cell DNA.
Ultraviolet radiation is used to irradiate sun-beds,
so frequent users of sun beds are also increasing
their risk of skin damage - the lamps emit uv radiation which can
cause DNA damage leading to cancer.
People who work outside or live in
particularly sunny climates, are at higher risk - though evolution
has allowed many people to have developed extra melanin in their
skin to increase uv protection - that's why so many people in sunny
areas like Africa have a much darker skin than many northern
European peoples.
Fair-skinned should use sun-blockers to
protect their skin in bright sunlight.
Viruses
Some types of cancer are triggered by particular
viral infections. See also
Communicable diseases
This is a communicable disease causing an
increase in the likelihood of
developing a non-communicable disease.
The hepatitis virus (hepatitis B and C
strains) causes long-term infections in the
liver where it inhabits the cells and this gives you an increased
chance of developing liver cancer.
The chance of becoming infected with this
communicable disease can depend on your lifestyle e.g.
contracting hepatitis during unprotected sex or drug users
sharing a needle.
The
human papillomavirus (HPV
virus) is a virus that
can infect the human reproductive system.
HPV is a communicable pathogen infection, BUT, is linked to
non-communicable diseases.
HPV infection occurs when the virus enters your body, usually
through a cut, abrasion or small tear in your skin. The virus is
transferred primarily by skin-to-skin contact. Genital HPV
infections are contracted through sexual intercourse, anal sex
and other skin-to-skin contact in the genital region.
It is thought that most cases of cervical
cancer arise from HPV infections - one disease causes another.
The HPV virus causes cervical warts.
