Snapshot A 26-year-old woman presents to the gynecology clinic with a mass in the left breast. She discovered this mass while showering. Her last menstrual period was 10 days ago. There is no family history of breast cancer. On physical exam, you palpate a 3 cm, firm, non-tender mass in the upper lateral quadrant of the left breast. The mass is smooth, well-circumscribed, and mobile. There are no skin changes, nipple discharge, or axillary lymphadenopathy. Ultrasound of the breast was carried out as shown. Introduction Clinical definition benign solid tumor of the breast with epithelial and stromal components Associated conditions breast cancer phyllodes tumor of the breast Prognosis natural history of disease patient presents with a small, firm, mobile, and non-tender breast lump most small tumors reabsorb rapid increase in size is a cause for concern giant forms (up to 15 cm) have malignant potential Epidemiology Incidence common in women 15-35 years of age second most common benign breast mass most common breast tumor in women under 30 Demographics mostly women in males may be associated with anti-androgen treatment Risk factors use of oral contraceptives pregnancy Etiology Pathophysiology unclear, but partially hormone dependent seen mostly during reproductive years increases during pregnancy regresses during menopause Presentation Physical exam firm painless freely movable well circumscribed round breast mass 2-3 cm in diameter does not change with menstrual cycle ("unchanged for three months") grows slowly in response to estrogen vs rapid change of fibrocystic disease Imaging Ultrasonography indications initial diagnostic test for a breast mass in a female under 30 years of age findings reveals a hypoechoic mass with sharp margins can determine if the mass is cystic or solid Studies Fine needle aspiration or core biopsy of the mass to confirm diagnosis and/or exclude malignancy Histology proliferative breast lesions without atypia epithelial proliferation occuring in a single terminal ductal unit surrounded by a fibroblastic stroma basement membrane is intact Any enlarging mass warrants excision Differential Fibrocystic disease pain and tenderness varies with menstrual cycle ill-defined mass Breast cyst Galactocele key distinguishing factor appears cystic (smooth anechoic mass) on sonography Treatment Conservative observation indication small tumors with slow or no growth rate repeat breast exam and sonogram in 3-6 months Operative surgical excision indications tumors enlarging on follow-up initial presentation of a large mass patient's preference cryoablation an alternative to surgery indications visible on sonogram mass < 4 cm diagnosis confirmed by histology Complications May be a risk factor for future cancer if the fibroadenoma is complex positive family history of breast cancer