Cancer is not a single disease with a single cause or cure. Cancer is the result when cells divide uncontrollably and invade other nearby tissue in the body. Cancer spreads through the body by way of blood circulation or by the clear fluid that travels through the lymphatic system and carries cells that help fight infections and other diseases.
There are more than 100 types of cancers, but they are divided into the following main categories:
1. Carcinoma: Carcinoma is cancer that begins on the skin or in tissues that line or cover the internal organs.
2. Sarcoma: Sarcoma is cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective tissue.
3. Leukemia: Leukemia is cancer that starts in blood-forming tissue such as the bone marrow and causes large numbers of abnormal blood cells to be produced that then enter the bloodstream.
4. Lymphoma and myeloma: Lymphoma and myeloma are cancers that begin in the cells that make up the immune system.
The body is made up of many different types of cells. Cells grow and divide in a normal and controlled way to produce more cells as they are needed. When cells get old or are damaged, they die and then they are replaced with new cells.
When this normal process goes wrong (the genetic material - DNA - of a cell becomes damaged or changed) the body begins producing mutations that affect normal cell growth. The result is that cells don't die when they should, and new cells form when the body doesn't need them. These extra and mutated cells then can form a mass of tissue that is called a tumor.
All tumors are not cancerous. Most tumors are benign. "Benign" means that the tumor is not cancerous. Tumors that are cancerous are called "malignant" tumors.