Breast cancer in women under 50: Most are not high risk.

Background: In 2009, the United States Preventive Services Task Force changed the recommended starting age for annual screening mammography from 40 to 50 for non-"high risk" women. In 2015, the American Cancer Society issued similar guidelines, with a starting age of 45. Our hypothesis is that most women diagnosed with breast cancer in this age group do not fall into a "high risk" category.