What is Cancer?
The human body is made up of billions of cells that group together to form the component parts of the body. Each cell has a nucleus that contains the genes that control the cell and govern what it does, when it will reproduce and when it will die.
Cells reproduce by dividing; a single cell divides to form two identical cells which divide to form four, which divide to form eight, which divide to form sixteen and so on. The new cells remain in the same area of the body and mature to take on the same function as the original cell. This process is normally well-ordered but occasionally breaks down and cells continue reproducing out of control. This unregulated production of cells causes a build-up of abnormal cells forming a lump or tumor.
Tumors are either benign or malignant. Benign tumors (noncancerous) are made up
of abnormal cells that are similar to normal cells and often have a covering of normal cells. Benign tumors are usually slow-growing, do not invade surrounding tissue and do not spread to other parts of the body. Benign tumors are not normally life-threatening unless they impact on the function of vital organs or
structures by applying pressure on them.
Malignant (cancerous) tumors are made up of cancer cells which, unlike normal cells, do not become specialized in nature, reproduce without stopping, invade and destroy surrounding tissue and spread to other parts of the body. It is this uncontrolled growth, with the invasion and destruction of tissue and ability to spread locally and throughout the body via the blood stream or lymphatic systems that makes cancer so destructive.
Cancers are normally named according to the location of the organ in which they originate; e.g., lung or breast cancer, but are also given the following names according to where the cancer cell started:
- Carcinoma – the majority (about 90%) of cancers that start in the skin or tissue covering internal organs, including organs such as the liver, lungs and kidneys, which are derived from the endodermal (inside) and ectodermal (outside) surface layers of the embryo
- Central nervous system – cancers that start in the tissues of the brain or spinal cord
- Leukemia – cancer that starts in blood-producing tissue
- Lymphoma – cancer that begins in the lymphocytes that are responsible for the immune system
- Sarcoma – cancer that starts in the connective tissues, such as bone, fat, muscle, cartilage, blood vessels or other supportive tissues, which are derived from the mesoderm (middle cell layer) of the embryo