Cancer is an uncontrolled growth of the cells in any part of the body. This growth interferes with the way your body normally functions. There are many kinds of cells that make up the tissue in a human body. Cells make new cells by dividing. Some cells stop dividing when they become adult cells. Other cells constantly divide, such as those of your skin, hair, and blood. Some divide only if there has been damage somewhere in your body. They "turn on" only until the damage has been repaired. Cancer tissues have lost their ability to "turn off" their growth. They eventually crowd out healthy tissues, disrupting your body's ability to do what it needs to do. There are over 100 different kinds of cancer.

When cancer spreads, though, it is still named after the part of the body where it started. For example, if prostate cancer spreads to the bones, it is still prostate cancer, and if breast cancer spreads to the lungs it is still called breast cancer. Leukemia, a form of cancer, does not usually form a tumor. Instead, these cancer cells involve the blood and blood-forming organs (bone marrow, lymphatic system, and spleen), and circulate through other tissues where they can accumulate. It is important to realize that not all tumors are cancerous. Benign (noncancerous) tumors do not metastasize and, with very rare exceptions, are not life-threatening.

Cancer is classified by the part of the body in which it began, and by its appearance under a microscope. Different types of cancer vary in their rates of growth, patterns of spread, and responses to different types of treatment. That's why people with cancer need treatment that is aimed at their specific form of the disease. In America, half of all men and one-third of all women will develop cancer during their lifetimes. Today, millions of people are living with cancer or have been cured of the disease. The risk of developing most types of cancer can be reduced by changes in a person's lifestyle, for example, by quitting smoking or eating a better diet. The sooner a cancer is found, and the sooner treatment begins, the better a patient's chances are of a cure.

Many people will get some form of cancer in their lifetime. The good news is that almost half (4 in 10) of them will be cured for at least five years. Your chances of being cured increase greatly with getting an early, accurate diagnosis, quickly starting the appropriate treatment, and getting follow-up evaluations. The most common ways of treating cancer are with surgery, radiation therapy, chemotherapy, hormone therapy, and immunotherapy. These can be used alone or in combination. There are new therapies being developed every day by researchers looking for better options for cancer patients. Research is also being done in the area of preventing cancer.