Definition of Cancer
Cancer is a group of many different diseases that have some important things in common. They all arise in cells, the body's basic unit of life. To understand different types of cancer, it is helpful to know about normal cells.
Normally, cells grow and divide to produce more cells only when the body needs them. This orderly process helps keep the body healthy. But sometimes cells keep dividing when new cells are not needed. These cells may form a mass of extra tissue called a growth or tumor. Tumors can be benign or cancerous.
Benign tumors are not cancer. They can usually be removed, and in most cases, they don't come back. Most important, the cells in benign tumors do not invade other tissues and do not spread to other parts of the body. Benign breast tumors are not a threat to life.
Cancerous tumors can be non-malignant (meaning that they have not spread from their primary location) or malignant (meaning that cells in these tumors have invaded other tissues and organs. Also, cancer cells can break away can metastasize from a primary tumor and enter the bloodstream or lymphatic system. That is how breast cancer spreads and forms secondary (malignant) tumors in other parts of the body. The spread of cancer is called metastasis.
