Cancer
Cancer is essentially a disease of mitosis - the normal 'checkpoints' regulating mitosis are ignored or over-ridden by the cancer cell. Cancer begins when a single cell is transformed, or converted from a normal cell to a cancer cell.
Cancer can be caused by agents called carcinogens, such as cigarette smoke, x-rays, nuclear radiation, UV light and some chemicals.
Carcinogens can cause a DNA mutation that occurs in one of several genes that normally function to control growth. E.g. the BRCA 1 gene, the "Breast Cancer Gene" normally functions to suppress tumor formation; but if a gene contains mutations such thatο BRCA1 does not work properly, tumor formation can begin (Note: mutations in this gene do not mean that a person will develop breast cancer, just that they have an increased risk for breast cancer).
Once these crucial Cell Cycle genes start behaving abnormally, cancer cells start to develop wildly by repeated, uncontrolled mitosis.
Tumors
The cancer cells grow and divide to form mass of cancer cells called a tumor. As the tumor grows larger, it begins to release proteins from the cell to attract new blood vessel growth.
Benign Tumors
Tumor cells remain at original site. They do not spread and usually cause little trouble. They can be removed surgically or killed by radiation, usually eliminating any further cancer development at that site.
Malignant Tumors
Malignant tumors are dangerous. The malignant cells grow squashing normal cells and preventing them working normally. Some tumor cells send out signals that tell the body to produce a new blood vessel at the tumor site. These cells not only have their own food and oxygen supply, they also have an avenue for escape to a new part of the body - through the new blood vessel and into bloodstream. Cells that break away from the tumor begin to spread to surrounding tissues (via the bloodstream or lymph) and start new tumors, this is called metastasis. Usually surgery is performed to remove the tumor, followed by radiation and chemotherapy.
