What is Cancer

Cancer is the name given to a large group of diseases, all of which have one thing in common: cells that are growing out of control. Normally, the cells that make up all of the parts of our bodies go through a predictable life cycle -- old cells die, and new cells arise to take their place. Occasionally, this process goes awry, and cells begin to multiply out of control. The end result is a tumor, a mass of cells.

A benign tumor is one that will not spread, or metastasize, to other parts of the body. It is considered noncancerous. A malignant tumor, on the other hand, can spread throughout the body and is considered cancerous. When malignant cells break away from the primary tumor and settle into another part of the body, the resulting new tumor is called either a metastasis or a secondary tumor.

There are several major types of cancers, including:

• carcinomas, which form in the cells that cover the skin or line the mouth, throat, lungs and organs
• sarcomas, which are found in the bones, muscles, fibrous tissues, and some organs
• leukemias, which arise from white blood cells in the blood and bone marrow
• lymphomas, which arise in lymphocyte cells in the blood, spleen, and lymph nodes.

Cancer may take years to develop. The process typically begins with some disruption to the DNA of a cell, the genetic code that directs the life of the cell. Such disruptions can be caused by many things, such as diet, tobacco, sun exposure, or certain chemicals. Some cells will enter a precancerous phase, known as dysplasia. Some cells will also enter the state of carcinoma in situ, in which the cancer cells are restricted to a microscopic site and do not pose a great threat. Eventually, unless the body's own immune system takes care of the wayward cells, a tumor will develop. It may take as long as 30 years for a tumor to go through the entire process and become large enough to produce clinical symptoms.

Anyone can get cancer, including children, but it is most common in people over the age of 50. This year about 1.22 million people in the United States will be diagnosed with cancer (not including the more than 1 million annual cases of basal and squamous-cell skin cancers.) About 563,000 people will die of cancer this year.