Snap Shot A 28-year-old female recently discovered a lump in her right breast. She has no family history of breast cancer, and her menstrual cycle began at 13 years of age. On exam you find a 1-cm movable mass in the right outer/upper quadrant. There is no skin dimpling. A mammogram is shown. Introduction Most common cause of benign breast masses in premenopausal women Caused by exaggerated response to hormones and fluctuations in mass size Not typically associated with progression to cancer Several histologic types fibrosis breast stromal hyperplasia cystic may show large or small cysts "blue domed" ductal dilation sclerosing adenosis acini proliferation with intralobular fibrosis associated with calcifications commonly mistaken for infiltrating ductal cancer ductal/epithelial hyperplasia epithelial cell proliferation in terminal duct lobule ↑ risk of carcinoma with atypical cells secondary to estrogen stimulation Presentation Symptoms bilateral breast pain or tenderness size/pain varies with the menstrual cycle