what is cancer?

Cancer is the general name for a group of more than 100 diseases in which cells in a part of the body begin to grow abnormally and out of control.

Normal body cells grow, divide, and die in an orderly fashion. During the early years of a person's life, normal cells divide more quickly, resulting in body growth.

Once the person becomes an adult, cells in most parts of the body divide only to replace worn-out or dying cells and to repair injuries.

Cancer cells develop because of damage to DNA—a substance that exists in every cell and directs all of the cells’ activities. A cell’s DNA can be damaged by a person’s poor eating habits; external (work, family) and internal (emotional) stresses; and things in the environment such as viruses, first- or second-hand tobacco smoke, and chemicals in food, cleaning products, the air, etc.

Most of the time, when DNA becomes damaged, the cell either dies or is able to repair the DNA. In cancer cells, however, damaged DNA is not repaired.

Abnormal and cancerous cells are constantly growing and dividing, and when the immune system is compromised, they are usually able to outlive normal cells. Over time, they form into groups known as lumps, masses, or tumors.

Some cancers, like leukemia, do not form tumors. Instead, these cancer cells involve the blood and blood-forming organs and circulate through other tissues, where they grow.

Cancer cells often travel through the bloodstream or lymph system to other parts of the body, where they grow and replace normal tissue. This spreading process is called metastasis.

Even when cancer has spread to a different part of the body, it is still named for the place where it started.

Breast cancer that has spread to the liver is metastatic breast cancer, not liver cancer. Prostate cancer that has spread to the bone is called metastatic prostate cancer, not bone cancer.

Different types of cancer can act very differently. For example, lung cancer and breast cancer grow at different rates and respond to different treatments. Specific types of cancer require specific treatments.

It is important to remember that not all tumors are cancerous. Benign (non-cancerous) tumors do not spread to other parts of the body and are rarely life threatening.

How common is cancer?

Today, millions of people are living with or have had cancer. Half of all men and 1/3 of all women in the US will develop cancer during their lifetime.