Cancer is a condition where one or more cells lose control and multiply chaotically. Normally, the body is able to regulate cell growth and ensure that cells form organized tissues according to an original blueprint contained in its DNA. However, DNA is easily damaged by radiation and other causes, producing defective DNA. When cells with this defective DNA go out of control it is officially called cancer.

A single cancerous cell can quickly divide into more, forming a growth of cancerous cells known as a tumor. A tumor tumor can be of two types, benign or malignant. Benign tumors do not spread through the body and typically remain in an isolated clump that can be surgically removed. Malignant tumors, however, invade the entire body, destroying healthy tissue and destroying vital organs. Malignant tumors are much more difficult to remove than benign tumors and often result in death.

A tumor has no real defined structure like the rest of the body and can contain any number of different cells. It may include muscle, fat, blood vessels, and nerves, yet none of these cells will serve any real purpose and will not really be coordinated with the rest of the body. One could refer to a tumor as a sort of parasite that uses a body's resources, yet does not contribute to any of the body's functions.

Cancerous tumors can range in size from very small to very large. Figure 1.1 shows a perfect example of how large a tumor can get. In this case, the tumor was embedded in a person's chest cavity and appears to be mostly benign. Most tumors do not reach this size and can be as small as a mole on your skin (and might be mistaken as one). Benign tumors can usually be left in place without surgery until they get so large that they prevent or cripple normal bodily function. Malignant tumors, on the other hand, need to be dealt with immediately to prevent spreading to vital areas of the body.

The causes of cancer are diverse since many things can cause mutations in DNA. The most effective cause is ionizing radiation, which penetrates the cells and causes changes in the molecular structure of the DNA. However, this type of radiation is rarely encountered in sufficient quantitities to cause cancer. Other causes include excessive sunlight (Ultraviolet radiation), certain foods, and the ingestion or inhalation of carcinogens. Carcinogens are substances known or suspected to cause cancer, such as asbestos and cigarette fumes.

Prevention of cancer is pretty much impossible, although you can reduce your chances of getting cancer. You can avoid skin cancer (melanoma) by not taking in excessive amounts UV radiation from sunlight and tanning booths. By not smoking tobacco, you can greatly reduce your risk of getting lung, mouth, or throat cancer. Some people believe that specific foods cause cancer, although we have yet to see any strong evidence to support their theories.

If you suspect that you have cancer, you should immediately report to a physician. You can watch for cancer by feeling for suspicious lumps on your skin and looking for any moles that dramatically change appearance. A doctor will easily be able to tell if the growth is in fact cancerous and suggest treatment.

There is still no great cure for malignant cancer, although science has developed several treatments that do work most of the time. The first obvious treatment is surgical removal of the tumor, but this cannot always be accomplished since a tumor might be unreachable or could have invaded a vital organ. In such a case, doctors can use either chemotherapy or radiation treatment. Chemotherapy involves injecting the patient with toxic chemicals with the intent of killing the cancerous growth. Unfortunately, the patient becomes very ill as a side effect, often losing all of their hair. Radiation treatment involves placing a very small point source of radiation next to the tumor to try to kill the tissue. Both methods only work sometimes and are not 100% reliable.