Twenty-eight-year-old woman with incidental mass on US (performed to evaluate right breast pain) initially diagnosed as tubular adenoma (TA), but on our retrospective review reclassified as nodular adenosis. Her mother and maternal aunt were diagnosed with breast cancer at ages 49 and 55, respectively. A: Antiradial (top left), radial (top right), and Doppler (bottom left) US images show an oval, parallel, hypoechoic 5 × 2 × 5 mm mass with microlobulated margins and internal vascularity (arrows) at 1 o'clock position, 5 cm from the nipple, BI-RADS 4A. US-guided 14-g core-needle biopsy histopathology (B) (4×, hematoxylin and eosin, 4× close-up on right) revealed nodular adenosis with densely packed tubules (arrows) that, at the margins, blend in with surrounding tissue; this is less discrete than a TA.