Dense breast tissue, which is common, and normal (seen in about 40% of women screened), can mask detection of breast cancer on mammography. Ultrasound is known to improve invasive cancer detection after standard mammography in women with dense breasts. Tomosynthesis (3D mammography) improves cancer detection compared to standard mammography. It is not known whether ultrasound would still be of benefit or not after tomosynthesis in women with dense breasts. Opened in December 2015, the purpose of this study is to determine the added cancer detection yield (if any) when screening ultrasound is added to 3D mammography in women with dense breasts. Women will undergo three annual rounds of screening. The cost of the screening ultrasound is covered by the study, funded by the National Cancer Institute and the Pennsylvania Breast Cancer Coalition. The study will accrue 6200 women aged 40-75 across UPMC and non-UPMC sites in Western Pennsylvania and is expected to complete accrual in March 2018. Interested patients can contact Nicole Lettiere at 412-641-8283 or Dr. Wendie Berg, firstname.lastname@example.org.