What Is Breast Cancer?

Each month, a woman's breasts go through temporary changes associated with menstruation, and a lump may form.  While the vast majaority of these growths are not cancerous, any lump should be examined immediately.  

Lumps are most common in the lobules -- small sacs that produce milk -- or the ducts that carry milk to the nipple.  But they occasionally start in other tissue.  The two main categories of breast cancer are lobular and ductal carcinomas. 

Breast cancer usually begins with the formation of a small, confined tumor. Some tumors are benign, meaning they do not invade other tissue; others are malignant, or cancerous. Malignant tumors have the potential to metastasize, or spread. Once such a tumor grows to a certain size, it is more likely to shed cells that spread to other parts of the body through the bloodstream and lymphatic system. Different types of breast cancer grow and spread at different rates; some take years to spread beyond the breast, while others move quickly.

Men can get breast cancer, too, but they account for less than one-half of one percent of all cases.  Among women, breast cancer is the most common cancer and the second leading cause of cancer deaths -- behind lung cancer.

If eight women were to live to be at least 85, one of them would be expected to develop the disease at some point during her life.  Two-thirds of women with breast cancer are over 50, and most of the rest are between 39 and 49. 

Fortunately, breast cancer is very treatable if detected early. Localized tumors can usually be treated successfully before the cancer spreads; and in nine in 10 cases, the woman will live at least another five years.  Experts usually consider a five-year survival to be a cure. 

Once the cancer begins to spread, getting rid of it completely is more difficult, although treatment can often control the disease for years.  Improved screening procedures and treatment options mean that at least seven out of 10 women with breast cancer will survive more than five years after initial diagnosis, and half will survive more than 10 years. 

What Causes Breast Cancer?

Although the precise causes of breast cancer are unclear, we know what the main risk factors are. Still, most women considered at high risk for breast cancer do not get it, while many who do have no known risk factors.  Among the most significant factors are advancing age and a family history of breast cancer.  Risk increases slightly for a woman who has had a benign breast lump and increases significantly for a woman who has previously had cancer of the breast or the ovaries. 

A woman whose mother, sister, or daughter has had breast cancer is two to three times more likely to develop the disease, particularly if more than one first-degree relative has been affected.  Researchers have now identified two genes responsible for some instances of familial breast cancer -- called BRCA1 and BRCA2.  About one woman in 200 carries it.  Having the gene predisposes a woman to breast cancer but does not ensure that she will get it.