The words "you have cancer " must have been one of the most difficult things you've ever heard. And like most patients, once reality sets in, you want as much information on the disease as possible. While this information should be useful to you, it cannot replace the advice and information given to you by your doctor. Seek your doctor's counsel—and that of your entire treatment team—throughout your illness.

What is cancer?

To understand cancer, it is helpful to know how normal cells become cancerous. The body is made up of many types of cells. Normally, cells grow, divide and produce more cells to keep the body healthy and functioning properly. Sometimes, however, the process goes astray—cells keep dividing when new cells are not needed. The mass of extra cells forms a growth or tumor. Some types of cells are more prone to abnormal growth than others. Tumors can be benign or malignant.

Benign tumors, however, are not cancer. They often can be removed and, in most cases, they do not come back. Cells in benign tumors do not spread to other parts of the body. Most important, benign tumors are rarely a threat to life.

Malignant tumors, however, are cancer. Cells in malignant tumors are abnormal and divide without control or order. These cancer cells can invade and destroy the tissue around them. Cancer cells can also break away from a malignant tumor and enter the bloodstream or lymphatic system vessels (the two systems of vessels that bathe and feed all of the body's organs). This process, called metastasis, is how cancer spreads from the original tumor to form new tumors in other parts of the body.

Can cancer be prevented?

Cancer develops gradually as a result of a complex mix of factors related to environment, lifestyle and heredity. Scientists have identified many factors that increase the chance of getting cancer. Some people are more sensitive than others to factors that can cause cancer.

Many cases of cancer can be prevented by not using tobacco products, avoiding harmful rays of the sun and choosing foods with less fat and more fiber. In addition, alcohol and exposure to certain chemicals and/or radiation may increase a person's risk of developing cancer.

While many risk factors can be avoided, others, such as inherited factors, are unavoidable. It is helpful to be aware of them, but it is also important to keep in mind that not everyone with a particular risk factor for cancer actually gets the disease. In fact, most do not. People who have an increased likelihood of getting cancer can help protect themselves by avoiding risk factors where possible and by getting regular checkups so that, if cancer develops, it is likely to be found early. Treatment is likely to be more effective when cancer is detected early.

How is cancer treated?

Cancer may be treated with surgery, radiation therapy, chemotherapy, hormone therapy or biological therapy. The doctor may use one method or a combination of methods. The choice of treatment depends on the type and location of the cancer, whether the disease has spread, the patient's age and general health, and other factors.