Cancer is a disease that starts in our cells. Our bodies are made up of million of cells, grouped together to form tissues and organs such as muscles and bones, the lungs and the liver. Genes inside each cell order it to grow, work, reproduce and die. Normally, our cells obey these orders and we remain healthy.
But sometimes the instructions in some cells get mixed up, causing them to behave abnormally. These cells grow and divide uncontrollably. After a while, groups of abnormal cells form lumps, or tumors.
Tumors can be either benign (non cancerous) or malignant (cancerous). Benign tumor cells stay in ne place in the body and are not usually life-threatening.
Malignant tumors cells are able to invade nearby tissues and spread to other parts of the body. Cancer cells that spread to other parts of the body are called metastases.
The first sign that a malignant tumor has spread (metastasized) is often swelling of nearby lymph nodes, but cancer can spread to almost any part of the body. It is important to find and treat malignant tumors as early as possible. Cancers are named after the part o the body where they start. For example Melanoma that starts in the skin but spreads to the liver is called Melanoma with liver metastases. (Melanoma: Understanding your diagnosis. Canadian Cancer Society 2008)