American Cancer Society, American College of Radiology, the Society of Breast Imaging and American College of Obstetricians and Gynecologists still recommend getting your first mammogram, an X-ray of your breasts, at 40.

Pan-Canadian Study of Mammography Screening and Mortality from Breast Cancer
A Pan Canadian study involving more than 2.7 million women showed a reduction in breast cancer mortality for the screened population. An analysis of 7 out of 12 Canadian screening trials which represented 85% of the population demonstrated a 40% reduction in breast cancer mortality. This study contradicts the paper which reported the 25 year results of the Canadian National Breast Screening Study which followed nearly 90,000 women and no mortality reduction was found.