Breast Cancer
Breast Cancer, malignant tumor in the glandular tissues of the breast . Such tumors, also called carcinomas , form when the processes that control normal cell growth break down, enabling a single abnormal cell to multiply at a rapid rate. Carcinomas, which tend to destroy an increasing proportion of normal breast tissue over time, may spread, or metastasize, to other parts of the body. Scientists do not understand exactly what causes breast cancer. Studies suggest that several categories of women are at increased risk for the disease: those with a long menstrual history (menstrual periods that started before age 12 and ended after age 50); those who never gave birth or who waited until after age 30 to have children; and those who have used birth control pills or hormone replacement therapy. Such risk factors, all of which relate to hormone-based life events, suggest that breast cancer is somehow affected by prolonged exposure to female sex hormones, such as estrogen . X-ray examinati