The basics of UV sun rays

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Cancer in general

Cancer is a non-communicable (non-infectious) disease, in other words it is not caused

by pathogens.  Cancer is caused when abnormal cells in the body divide by mitosis in

an uncontrolled way by using the enzyme telomerase; this gives rise to tumours and, if

the cells are malignant, cancers.  Cancer is a major cause of death in the developed

world.  In 1999 7.3 million people worldwide died from cancers.  In high income

European countries cancer is known as the second biggest killer. There are over 200

different cancers.  The most common cancers are lung cancer and skin cancer.

There are about 42.2 new cases of lung cancer reported in the UK per 1000 people

each year and 5 new cases of skin cancer reported per 1000 people in the UK each

year - and many cases go unreported.  It is difficult to treat cancer because there are

many different cancers.  There are some common characteristics between them though;

one being the presence of unregulated cell growth leading to the development of

tumours.  Not all tumours are cancerous - the greatest numbers are benign.  Benign

tumours are characterised by entirely localised growth and are usually separated from

surrounding tissue by a surrounding capsule.  Benign tumours generally grow slowly and

closely resemble the structure of the tissue they originate from.  At worst benign tumours

may press on blood vessels or nerves, interfering with their normal function.  Cells from

malignant tumours, however, invade other tissues, causing considerable damage; they

metastasise - break off and spread to other parts of the body via the blood or lymph

system and form secondary growths in other organs.  A cancer becomes harder to treat

the more spread over your body it is.  Drugs can be given to reduce the rate of division

of the cancer cells and radiation treatment can be used to kill the cells.  Research is

continuing into several other methods of treating cancer.

Because cancer cells are slightly different from normal cells, both in behaviour and

appearance (wide variation in the shape and size of cell, large nucleus compared to

size of cell), white lymphocytes may recognise them as foreign and kill them, this

happens quite frequently in the body.  The cancers doctors detect in the body are the

ones that the bodies own defences have missed. To find out if a tumour is benign or

malignant a surgeon has to do a biopsy (remove a small sample of the tumour for

analysis).  Cancer cells, even when widely disseminated, may retain the physical and

biological characteristics of their tissue of origin, therefore a pathologist can often

determine the site of origin of metastatic tumours by microscopic examination of the

cancerous tissue.  The less closely a cancer resembles its tissue of origin the more

malignant and rapidly invasive it tends to be.  

The causes of cancer are still not fully understood.  Basically cancer is a genetic

process.  Something happens to change the way in which the cells behave.  This may

involve a change or mutation of the DNA in the nucleus of the cell.  Gene abnormalities

can be inherited or they can be induced in a body cell by a virus or by damage from an

outside source.  No more than 20% of cancers are based on inheritance.  In some

hereditary disorders the chromosomes exhibit a high frequency of breakage, such

diseases carry a high risk of cancer.  Viruses are the cause of many cancers in animals.  

Research indicates that such viruses may contain a gene called viral oncogene capable

of transforming normal cells to malignant cells.  Ionising radiation is a puissant cause of

cancer; it induces changes in DNA such as chromosome breaks and transpositions.  

Radiation acts as an initiator of carcinogens.  It is known chemical carcinogens are a

main cause of cancer.  Some chemicals act as initiators - inducing a change that

progresses cancer after a latent period of years, the delay provides opportunity for

exposure to other factors.  Initiators produce irreversible changes in DNA.  Some

chemical carcinogens are promoters - they increase synthesis of DNA and stimulate

expression of genes.  Tobacco smoke contains many initiators and promoters; alcohol

is an example of a promoter.  Carcinogenic chemicals also produce chromosome

breaks and translocations.  About 80% of cancers may be caused by environmental

factors.

There are seven symptoms that are early signs of cancer:

1.        Change in bowel or bladder habits

2.        A sore that does not heal

3.        Unusual bleeding or discharge

4.        Thickening or lump in the body somewhere

5.        Indigestion or difficulty in swallowing

6.        Obvious change in a wart or a mole

7.        Nagging cough or hoarseness

The earlier a cancer is diagnosed and treated the greater the chance of a cure.  The

biopsy remains the only definitive method for the diagnosis of a cancer.

Once a tissue diagnosis of cancer has been made, the extent/stage of the disease must

be evaluated because prognosis and appropriate treatment vary with the stage of the

disease.  For each type of tumour the stage (I, II, III or IV) is defined in terms of findings

with progressively more severe prognostic implications: small local tumour, more

extensive local tumour, regional lymph node involvement, and distant metastases.  The

clinical stage, defined by information prior to surgical exploration, is used to decide

appropriate initial treatment.

The traditional means of treating cancer are surgery, radiation and chemotherapy.  The

aim of surgery is to remove all of the malignant cells.  Many cancers, though, are at too

advanced stage at the time of diagnosis to permit cure by surgery.  However surgery

may help to relieve symptoms, as of obstruction, or to reduce the size of the tumour in an

effort to improve the response to subsequent radiation or chemotherapy.  Ionising

radiation, which may be either electromagnetic or particulate, is destructive to tissue.  

Tumours vary greatly in their sensitivity to radiation.  Radiation is useful when a tumour is

located where it cannot be removed because surgery would damage vital adjacent

tissue or because a tumour has begun to infiltrate adjacent structures that cannot be

sacrificed.  Preoperative radiation may rapidly sterilise the tumour cells and prevent

them from seeding at surgery.  It may also shrink the tumour and make surgery easier, or

shrink the tumour and make surgery easier, or shrink an inoperable tumour so that it

becomes operable.  Chemotherapy is useful for tumours that have spread beyond the

area accessible for surgery or radiotherapy.  A number of different types of anticancer

drugs are used, but nearly all work by interfering with DNA synthesis or function.  Rapidly

dividing cells are therefore more sensitive to chemotherapy.  Cancers have a larger

proportion of dividing cells than do normal tissues, in which stem, or replenishing, cells

are dormant and therefore resistant to drug effect.  The most rapidly proliferating normal

tissues are the bone marrow and the lining cells of the gastrointestinal tract.  These are

the most sensitive normal areas of chemotherapeutic effect and constitute the sites of

toxicity that will limit the tolerable dose of most drugs.

To be effectively treated, a tumour must be more sensitive than the normal tissue.  Some

tumours may be many times more sensitive, but many are only slightly more sensitive.  

Fortunately, the normal bone marrow cells can divide faster than malignant cells and thus

recover more rapidly.  This permits a repeat cycle of the drug before the tumour has re-

grown very much.  Repeated cycles can steadily deplete the tumour before resistance

occurs.  Two major problems limiting the usefulness of chemotherapy are toxicity and

resistance.  Techniques that avoid or control toxicity and reduce the risk of resistance

have steadily improved.  It is important to begin treatment as early as possible, to use

the optimal dose of the drug, and to repeat cycles as quickly as possible, while giving

the patient a chance to somewhat recover from toxicity.

The use of multiple drugs is effective.  Combination chemotherapy employs several

drugs (often three to six at a time); each is effective as a single agent.  The drugs used

have different mechanisms of action, making cross-resistance less likely and different

types of toxicity, so that each may be given at optimal dose without causing fatal

addictive toxicity.

Chemotherapy may be used with surgery or radiation as combined modality therapy.  It

is often used as an adjuvant, or helper, when surgery is the primary therapy.  As such it

is usually given after surgery.  This type of therapy has greatly increased the cure rate of

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breast cancer.  The major purpose of chemotherapy as an adjuvant is to kill of micro-

metastases that may have been established before surgery.  Recently, chemotherapy

has been used before surgery as a neoadjuvant.  This therapy has the same effect as

adjuvant chemotherapy but may also shrink a tumour, making it more easily operable.

Many cancers arising from tissues that are hormone dependants are responsive to

hormone manipulation.  Other approaches are still being researched for the treatment of

cancer.  The most important method for curing cancer though is preventive, for example

stopping tobacco use, better ...

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