What is cancer?

The body is made up of billions of cells that form our tissues and organs. In most organs, cells are replaced on a regular basis, allowing each organ to continue to function normally. During this process, cells that die are replaced by new cells.

How a tumor forms

Occasionally, cells are replaced by abnormal cells which grow in an uncontrolled way. As a result, there is an abnormal growth or lump of cells that form a tumor. As they increase in size, benign tumors can present as a lump in the breast.

Types of breast tumors

There are two types of breast tumors: noncancerous tumors (benign) and cancerous tumors (malignant).

Benign breast tumors are not cancerous and are made of tumor cells that don't spread outside the breast in which they appear.

Malignant breast tumors are cancerous and are made up of cells that have the ability to spread from the breast to other parts of the body. Because of their spread and growth in other organs, malignant breast tumors can interfere with normal body function and be life-threatening.

How breast cancer cells spread to other parts of the body

Breast cancer cells can metastasize or break away from the main malignant tumor and travel to other parts of the body. The blood and lymph are body fluids that can carry these cancer cells from the main tumor to other parts of the body, commonly to the bones, liver, lungs, and brain.

If breast cancer spreads or metastasizes to other body parts, it is still considered breast cancer in that new site. For example, if breast cancer spreads to the lungs, the tumor in the lung is not lung cancer but breast cancer that has metastasized.