Breast cancer occurs when cells within the breast undergo changes that cause it to grow and divide uncontrollably. The tumor that develops from this will destroy tissue around it. Usually breast cancer arises from the cells that form milk ducts, but less commonly, the milk glands themselves can be the source. Because the female breast is much larger and more developed, women are about 100 times more likely to develop breast cancer than men.
What is going on in the body?
A tumor in the breast does not stop the breast from changing with the menstrual cycle or pregnancy or producing breast milk. A tumor will, however, cause destruction of tissue within the breast. Spread of the tumor to other parts of the body can cause death.
Cancer of the breast can be detected when it grows large enough to either be felt or seen on a mammogram. The tumor may distort the shape of the breast or the texture of the skin as it becomes larger. This is because surrounding tissues become fixed to the tumor. The tumor can grow through the breast to the outer skin if left untreated.
Cancer cells can also enter specialized channels in the breast called lymphatics. Cancer cells travel through the lymphatics to the lymph nodes to form tumors distant from the breast. This most commonly occurs in lymph nodes under the armpit or within the chest. This may occur when the tumor has grown large, but it can also happen sooner.
Cancer cells can also spread, or metastasize, to other parts of the body through the bloodstream. This can occur when the tumor is large or small. These cells can travel to other tissues and form new tumors. Breast cancer is most often spread to the bones, lungs, brain, and liver. However, any tissue can be affected.