The human body is made of tiny building blocks called cells. Your body creates them, replacing those that die with new ones. Usually, the body creates healthy, normal cells that do just what they’re supposed to do. This includes cells in the breasts, the two rounded areas on the front of the chest.
But if a cell changes into an abnormal, sometimes harmful form, it can divide quickly over and over again without dying, making many, many copies of itself. When this happens, a tumor, abnormal body cells grouped together in the form of a mass or lump, can start to form and grow.
Breast cancer is a kind of tumor that develops in the cells of a person’s breast. You may think that only women can get breast cancer, but because all people have breast tissue, men can get breast cancer as well – though this is very rare.
A tumor can form anywhere in a person’s body. Someone has cancer when those abnormal cells will not stop growing, and then cause sickness in the body. Someone with breast cancer may have cancer cells in just one part of the breast, which might be felt as a lump. The cancer can spread throughout one or both breasts. Sometimes breast cancer spreads to other parts of the body, like the bones, the liver, or elsewhere.
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Source: Symptom Of Breast Cancer