Cancer is a group of different diseases that have one important thing in common. They all arise in the most basic unit of life, the cells. The body is made up of many types of cells that grow and divide to produce more cells -only when the body needs them. This orderly process helps keep the body healthy. 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 malignant.

• Benign tumors are non cancerous. They can usually be removed, and in most cases, they don't come back. Most importantly, the cells in benign tumors do not invade other tissues or spread to other parts of the body. Benign breast tumors are not a threat to life.
• Malignant tumors are cancerous. Cells in these tumors can invade and damage nearby tissues and organs. Also, cancer cells can break away from a malignant tumor and enter into the bloodstream or lymphatic system. That is how breast cancer spreads and forms secondary tumors in other parts of the body. The spread of cancer is called metastasis.

The Breasts:

Each breast has 15 to 20 overlapping sections called lobes. Within each lobe are many smaller lobules, which end in dozens of tiny bulbs that can produce milk. Thin tubes called ducts link the lobes, lobules and bulbs. These ducts lead the nipple in the center of a dark area of skin called the areola. Fat fills the spaces around the lobules and ducts. There are no muscles in the breast, but muscles lie under each breast and cover the ribs.

Each breast also contains blood vessels and vessels that carry colorless fluid called lymph. The lymph vessels lead to small bean shaped organs called lymph nodes. Clusters of lymph nodes are found near the breast in the axilla (under the arm), above the collarbone, and in the chest.
Lymph nodes are also found in many other parts of the body.