The body is made up of many types of cells. Normally, cells grow, divide and die. Sometimes, cells mutate (change) and begin to grow and divide more quickly than normal cells. Rather than dying, these abnormal cells clump together to form tumors.

If these tumors are cancerous (also called "malignant"), they can invade and kill your body's healthy tissues. From these tumors, cancer cells can metastasize (spread) and form new tumors in other parts of the body. By contrast, noncancerous tumors (also called "benign") do not spread to other parts of the body.

There are many different types of cancer, but all cancers begin with abnormal cells growing out of control. The type of cancer is determined by where the growth of abnormal cells begins.

The most common cancers in adults are:

Skin cancer is the most common form of cancer. Fortunately, it is also the most curable.

There are 2 forms of skin cancer:

More than 1 million people will be diagnosed with skin cancer this year. Most will have non-melanoma skin cancer. Almost all skin cancers are the result of too much exposure to ultraviolet light, which is in sunlight and in lights used in tanning salons.

The majority of melanomas appear as moles - usually irregular in shape and colour and with a history of progressive change. Most melanomas are without sensation, although some are reported as itching and a minority may also bleed. An early melanoma, however, may look completely unremarkable.

About 50% of melanomas develop in existing moles and 50% as new moles.

As a rule, the public - particularly those in higher risk groups - should monitor their moles and seek advice from an expert if any are new, changing or 'atypical'.

The ABCDE rule (see right) can help you remember what to look for when you're checking any moles on your skin. If you notice any of these signs, talk to your doctor straight away.

Prostate cancer can grow quickly and spread to other parts of the body, or it can grow slowly and stay in the prostate.

Although men of any age can get prostate cancer, it is found most often in men over the age of 50. Three out of 4 cases of prostate cancer are the slow-growing type that causes few, if any, problems.

There are two ways that a doctor may examine your prostate. One is via a digital rectal exam. A normal prostate feels firm. If there are hard spots on the prostate, your doctor may suggest additional testing to check for prostate cancer.

Another way to check for prostate cancer is with a blood test called the PSA test. Men who have prostate cancer may have a higher level of PSA in their blood. However, the PSA level can also be high because of less serious causes, such as infection or prostate enlargement.

There are two main types of primary lung cancer:
Non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC).

Small Cell Lung Cancer accounts for about 20 out of every 100 lung cancers. It is so called because the cancer cells are small.

There are three main types of Non-Small Cell Lung Cancer :

Mesothelioma
Mesothelioma is a less common type of cancer that can affect the covering of the lungs (the pleura). It often occurs in people who have been exposed to asbestos.

Most colorectal cancers begin as a polyp.

At first, a polyp is a small, harmless growth in the wall of the colon. However, as a polyp gets larger, it can develop into a cancer that grows and spreads.

Warning signs of colorectal cancer may include blood in your stool or in the toilet after you have a bowel movement, a change in the shape of your stool and/or cramping pain in your lower stomach.

You should see your doctor if you have any of the warning signs of colorectal cancer.

Breast cancer begins in breast tissue. Most of the tumors that develop in breast tissue are benign. Some breast tumors are cancerous, but have not yet spread to other parts of the body.

This type of breast cancer is called "in situ" and it can almost always be cured with treatment.

The most serious type of breast cancer is "invasive", meaning that the cancerous tumors have spread to other parts of the body.

Breast cancer is the second most common cancer among women (behind skin cancer). The good news is that the rate of death from breast cancer has declined over the last few years.

This is probably because more tumors have been found early, when treatment can help the most. Mammograms and breast exams (both self-exams and exams by a doctor) can help find breast cancers early.

It is important to note that breast cancer is not a disease that purely affects women, but in certain cases it can also affect men. Click here for more information [Breast Cancer in Men]

Testicular cancer begins in one or both of the testicles. The testicles are located in the scrotum, the skin “sack” that hangs beneath the penis. They manufacture male hormones and produce sperm. A normal adult testicle is about the size of a golf ball and is round, smooth and firm.

Testicular cancer is more common in men who have a testicle that has failed to descend. In the unborn child the testicles develop inside the abdomen between the kidneys and descend into the scrotum at birth or during the first year of life. If this does not happen, the risk of a man developing testicular cancer is increased.

There are two main types of testicular cancer – seminomas and teratomas. They may be called germ cell tumours. Occasionally testicular tumours can be a mix of both types.

Around 2000 men a year are diagnosed with testicular cancer in the UK. It is not known exactly what the causes are, but research is going on all the time to attempt to establish them.

Ovarian cancer is cancer on one or both of the ovaries. The ovaries produce eggs, and the female hormones estrogen and progesterone. There are several types of tumors that can grow in or on the ovaries. The type of tumor depends on where it began growing and whether or not it is cancerous. Unfortunately, ovarian cancer is very hard to detect at an early stage. Your doctor may check your ovaries during your routine pelvic exam to see if they feel normal, but many times the tumors are so small they can't be detected.

A Pap smear is usually not able to find endometrial or ovarian cancer. The Pap smear checks for cervical cancer, which is less common than either endometrial or ovarian cancer. Cervical cancer was once more common, but early detection of cervical changes with the Pap smear has had a big impact.

Lymphoma is a cancer of the lymphatic system. The lymphatic system is made up of a series of vessels and glands, known as lymph nodes. These are spread throughout your body, much like your blood vessels.

The lymphatic system is part of your immune system.
It carries lymph around your body. Lymph is a fluid full of infection-fighting white blood cells known as lymphocytes. In lymphoma, these lymphocytes begin reproducing in an abnormal manner and begin to collect in certain parts of the lymphatic system, such as the lymphatic nodes. The affected lymphocytes begin to lose their infection-fighting properties, making you more vulnerable to infection. The causes of lymphoma are still unknown.

There are two main types of lymphoma:

Leukaemia is a cancer of the blood or bone marrow characterised by an abnormal increase of blood cells, usually leukocytes (white blood cells).

It can develop quickly (acute), or more slowly (chronic). Depending on the type of white blood cell affected, most acute leukaemia is either acute lymphoblastic leukaemia (ALL) or acute myeloid leukaemia (AML). Chronic leukaemia is usually either chronic lymphocytic leukaemia (CLL) or chronic myeloid leukaemia (CML). However there are also several less common types of leukaemia.

In acute leukaemia, immature white blood cells accumulate in the body and can disrupt the function of many tissues and organs. Cells in chronic leukaemia are slightly abnormal and do not function as well as they should.

Leukaemia is the ninth most common cancer in men in the UK and the eleventh most common cancer in women in the UK. There are about 7,000 new cases in the UK each year and more men are affected than women. It is the most common form of childhood cancer, but is ten times more common in adults.

Not everyone diagnosed with leukaemia will need treatment immediately, and some patients never require treatment (CLL, for example, can progress so slowly in some older people that they are more likely to die from other problems first). However, for those who do, the earlier it begins the more effective it is.

Treatment for acute leukaemia can include chemotherapy (anti-cancer drugs), steroids, radiotherapy, intensive treatments (including bone marrow or stem cell implant) and growth factors (substances that stimulate the bone marrow to make blood cells). Treatment for chronic leukaemia can also include biological therapy, such as interferon alpha.

Prognosis and survival from leukaemia varies enormously, and depends on factors such as the type of leukaemia you have, how advanced it was when first diagnosed, how well it responds to chemotherapy treatment, and how generally fit you are. Each person should discuss this individually with the team in charge of their care.