cancer - a definition
(KAN-sir)
The term for diseases in which the body's cells become abnormal and divide without control. Cancer cells may invade nearby tissues. And they may spread through the bloodstream and lymphatic system to other parts of the body. There are many different types of cancers, but all share one hallmark characteristic: unchecked growth that progresses toward limitless expansion.
Cancer is a scary word. Almost everyone knows someone who got very sick or died from cancer. Most of the time, cancer affects older people. Not many kids get cancer, but when they do, very often it can be treated and cured.
Being diagnosed with cancer can be frightening. But understanding what's going on inside your body can help you feel more in control of your disease.
Cancer is a disease that starts in our cells. Our bodies are made up of millions of cells, grouped together to form tissues and organs such as muscles and bones, the lungs and the liver. Genes inside each cell order it to grow, work, reproduce and die. Normally, our cells obey these orders and we remain healthy. But sometimes the instructions get mixed up, causing the cells to form lumps or tumours, or spread through the bloodstream and lymphatic system to other parts of the body.
Tumours can be either benign (non-cancerous) or malignant (cancerous). Benign tumour cells stay in one place in the body and are not usually life-threatening.
Malignant tumour cells are able to invade nearby tissues and spread to other parts of the body. Cancer cells that spread to other parts of the body are called metastases.
The first sign that a malignant tumour has spread (metastasized) is often swelling of nearby lymph nodes, but cancer can metastasize to almost any part of the body. It is important to find malignant tumours as early as possible.
Cancers are named after the part of the body where they start. For example, cancer that starts in the bladder but spreads to the lung is called bladder cancer with lung metastases.
Different Kinds of Cancer
Carcinomas, the most common types of cancer, arise from the cells that cover external and internal body surfaces. Lung, breast, and colon are the most frequent cancers of this type in the United States.
Sarcomas are cancers arising from cells found in the supporting tissues of the body such as bone, cartilage, fat, connective tissue, and muscle.
Lymphomas and Myelomas are cancers that arise in the lymph nodes and tissues of the body's immune system.
Leukemias are cancers of the immature blood cells that grow in the bone marrow and tend to accumulate in large numbers in the bloodstream.
Central nervous system cancers are cancers that begin in the tissues of the brain and spinal cord.
What Causes Cancer?
Cancer arises from a loss of normal growth control. In normal tissues, the rates of new cell growth and old cell death are kept in balance. In cancer, this balance is disrupted. This disruption can result from uncontrolled cell growth or loss of a cell's ability to undergo cell suicide by a process called "apoptosis". Apoptosis, or "cell suicide", is the mechanism by which old or damaged cells normally self-destruct.
Cancer begins with damage (mutations) in your DNA. Your DNA is like a set of instructions for your cells, telling them how to grow and divide. Normal cells often develop mutations in their DNA, but they have the ability to repair most of these mutations. Or, if they can't make the repairs, the cells often die. However, certain mutations aren't repaired, causing the cells to grow and become cancerous. Mutations also cause cancer cells to live beyond a normal cell life span. This causes the cancerous cells to accumulate.
The initial genetic mutation is just the beginning of the process by which cancer develops. Scientists believe you need a number of changes within your cells in order to develop cancer, including:
• An initiator to cause a genetic mutation. Sometimes you're born with this initial genetic mutation. Other times a genetic mutation is caused by forces within your body, such as hormones, viruses and chronic inflammation. Genetic mutations can also be caused by forces outside of your body, such as ultraviolet (UV) light from the sun or cancer-causing chemicals (carcinogens) in your environment.
• A promoter to cause rapid cell growth. Promoters take advantage of genetic mutations created by initiators. Promotors cause cells to divide rapidly. This could lead to a tumor. Promoters could be inherited, could come from inside your body or could come from outside your body.
• A progressor to cause cancer to become aggressive and spread. Without a progressor a tumor may remain benign and localized. Progressors make cancers more aggressive and more likely to spread. Like initiators and promoters, progressors could be inherited or they could come from environmental sources.
Your genetic makeup, forces within your body, your lifestyle choices and your environment can all set the stage for cancer or help complete the process once it's started. For instance, if you've inherited a genetic mutation that predisposes you to cancer, you may be more likely than other people to develop cancer when exposed to a certain cancer-causing substance. The genetic mutation begins the cancer process, and the cancer-causing substance could play a role in further cancer development. Likewise, smokers who work with asbestos are more likely to develop lung cancer than smokers who don't work with asbestos because the two carcinogens both play roles in cancer development.
Who Gets Cancer
Cancer doesn't discriminate when it comes to race, sex or age — anyone can get cancer. The ACS estimates that half the men and one-third of the women in the United States will develop cancer in their lifetimes. The ACS estimates that about 1.4 million new cases of cancer are expected in 2007, and about 560,000 people will die of the disease.
How common is cancer?
Half of all men and one-third of all women in the US will develop cancer during their lifetimes. Today, millions of people are living with cancer or have had cancer. The risk of developing most types of cancer can be reduced by changes in a person's lifestyle, for example, by quitting smoking, limiting time in the sun, being physically active, and eating a better diet. The sooner a cancer is found and treated, the better the chances are for living for many years.
What does Cancer look like?
The only way to diagnose cancer is to examine the cells under a microscope. Some imaging tests, such as computerized tomography (CT) or mammography, can indicate the possible presence of cancer by showing an abnormal mass, but cancer can be definitively diagnosed only by looking closely at the cancer cells under a microscope.
Your doctor uses a surgical process called a biopsy to get a sample of suspect tissue.
Under the microscope, normal cells look uniform, with similar sizes and orderly organization. Cancer cells look less orderly, with varying sizes and without apparent organization.
