Cancer is the uncontrolled growth of abnormal cells in the body. Cells grow and divide to help the body function properly. Under normal conditions, cell reproduction is carefully controlled by the body.
However, these controls can malfunction, resulting in abnormal cell growth. Old cells do not die and cells grow out of control, forming new, abnormal cells. These extra cells may cause the development of a lump, mass, or tumor. Some cancers involving the blood and blood-forming organs do not form tumors but circulate through other tissues where they grow.
A tumor may be benign (non-cancerous) or malignant (cancerous).
There are different main categories of cancer:
• Carcinomas begin in the skin or tissues that line the internal organs.
• Sarcomas develop in the bone, cartilage, fat, muscle or other connective tissues.
• Leukemia begins in the blood and bone marrow.
• Lymphomas start in lymphatic tissues (part of the immune system).
• Central nervous system cancers develop in the brain and spinal cord.
The type of cancer refers to the organ or area of the body where the cancer first occurred. Cancer that has metastasized to other areas of the body is named for the part of the body where it originated. For example, if breast cancer has spread to the bones, it is called “metastatic breast cancer” not bone cancer.
Cells from cancerous tumors can spread throughout the body. This process, called metastasis, occurs when cancer cells break away from the original tumor and travel in the circulatory or lymphatic systems until they are lodged in a small capillary network in another area of the body. Common locations of metastasis are the bones, lungs, liver, and central nervous system.
