Breast cancer incidence rates vary by age and location. BreastCancer. org reports that breast cancer incidence rates in the United States began decreasing in 2000 after increasing for the previous two decades. Some researchers believe the decrease was partially due to the reduced use of hormone replacement therapy (HRT). Even if breast cancer incidence rates in the U.S. are down overall, researchers at Washington University School of Medicine in St. Louis have found diagnoses of breast cancer have increased steadily in women under age 50 over the past two decades. For most women, regular breast cancer screening does not begin until at least age 40, so younger women diagnosed with breast cancer tend to have laterstage tumors and a more advanced disease. Similar findings have been noticed in Canada. An Ottawa-based study published in the Canadian Association of Radiologists Journal found that rates of breast cancer in women as young as their twenties have been increasing. The research…