They all have one common characteristic, however the uncontrolled growth and spread of abnormal cells that can invade and damage healthy body tissues and organs. Most cancers are named for the body tissue in which they begin, such as the breast, colon or skin. Normally, cells divide to produce new cells only when the body needs them. If cells keep dividing when new cells are not needed, a mass of extra tissue, called a tumor, forms. Tumors can be benign, meaning noncancerous, or malignant, meaning cancerous.
Cancer cells can break away from a malignant tumor and enter the bloodstream or lymphatic system.
This is how cancer spreads, or metastasizes, to other parts of the body. The process begins with the many thousands of genes found in each cell of the human body. Made up of DNA, genes carry instructions for making the proteins that regulate all body processes, including how efficiently we process foods, metabolize toxins, and fight infections. Genes are activated, or switched on and off, by signals in the body or by environmental influences. For instance, an unhealthy diet, cigarette smoke, too much sun, or high levels of certain chemicals, can damage the DNA and cause genes to mutate, or change.