Breast cancers are often found when a woman or her doctor feels a lump in the breast. Mammograms are special x-rays of the breast that can identify breast cancers before lumps are felt. The goal of screening mammograms is to identify breast cancers before they have spread. Recently, there has been much debate about whether mammograms decrease rates of death from breast cancer. The controversy is greatest for mammograms in women age 40 to 49 years. The Canadian Breast Cancer Screening study is a large study of screening (mammograms and breast examinations by doctors) for women in that age group. Seven to 10 years after the first screening visit, screening had not reduced deaths from breast cancer. However, some experts suggested that it would take longer than 10 years to demonstrate benefit from screening.