The best protection is early detection. Finding breast cancers early with mammography has also meant that many more women being treated for breast cancer are eligible for breast conservation therapy. When caught early, localized cancers can be removed without resorting to breast removal (mastectomy).
The main drawback of mammograms is that they aren’t perfect. Normal breast tissue can hide a breast cancer so that it doesn't show up on the mammogram. This is called a false negative. And mammography can identify an abnormality that looks like a cancer, but turns out to be normal. This "false alarm" is called a false positive. Besides worrying about being diagnosed with breast cancer, a false positive means more tests and follow-up visits, which can be stressful. To make up for these limitations, more than mammography is often needed. Women also need to practice breast self-examination, get regular breast examinations by an experienced health care professional, and, in some cases, also get another form of breast imaging, such as breast MRI or ultrasound.
For further facts and myths about breast cancer please see Myths/Facts of Breast Cancer Screening