The American Cancer Society defines breast cancer as a "malignant tumor that starts from the cells of the breast." The breast is made up of milk glands and fatty tissues, and cancer can occur in any of these tissues. Cells in our bodies are constantly reproducing, and when they start to reproduce at an abnormal rate, they cause a tumor to form. If cells from a malignant tumor enter the lymphatic system they can infect other tissues, this is termed as metastasizing. (more…)