In order to understand breast cancer, it's helpful to be aware of the basic anatomy of the breast. Each breast contains 15 to 20 lobes of tissue, arranged like the petals of a daisy. Lobes are further divided into milk-producing lobules, which are connected by ducts designed to carry milk to the nipple during breast feeding. Each breast also connects to lymph nodes in the underarm, above the collarbone, and in the chest behind the breastbone. As with other cancers, those that manifest in the breast start when something goes wrong in the body's normal cell dividing process. This causes an excess of cells to build up and form an abnormal lump of tissue, called a tumor. When this happens in the breast, it usually does so in the milk ducts, which is why it's called ductal carcinoma, or in the lobules, called lobular carcinoma. In 80% of cases, a tumor in any part of the breast will be found to be benign, or not cancerous. However, if a tumor is cancerous, it may grow and invade tissue nearby, like the chest wall, or it may spread to nearby lymph nodes or other organs. We know that breast cancer does not discriminate. From singers like Sheryl Crow and Melissa Etheridge, to actors like Christina Applegate and Cynthia Nixon, to political figures like judge Sandra Day O'Connor and first lady Nancy Reagan, the disease can strike anyone. Indeed, almost one in eight women will be diagnosed with breast cancer - but why does this happen? Researchers have found that the female hormone estrogen probably plays a role in the development of certain kinds of breast cancer. That's because estrogen tells cells to divide, and the more that cell division occurs, the more likely something will go wrong in that process. As a result, women who begin menstruating before 12, and those who go through menopause after 55 have a higher breast cancer risk. Similarly, women who undergo hormone therapy for menopause may be more likely to fall prey to cancer. In fact, the typical breast cancer patient is over 60 at the time of diagnosis. Many women who get breast cancer also have a history of the disease in their immediate families. And researchers now know that mutations on two genes, BRCA1 and BRCA2, are responsible for some cases of inherited breast cancer. One in 200 women carries these genes, which explains why up to 10% of breast cancer cases are related to BRCA. Still, there is no hard and fast rule about who will be affected by this disease! If you are concerned about breast cancer, make an appointment to speak with your doctor.