A 26-year-old white woman without risk factors for breast cancer had progressive enlargement of her left breast. There were no others symptoms. Physical examination revealed a large, painless, rubbery-firm, well-circumscribed, lobulated, mobile mass at the outer inferior quadrant of the left breast. There were no palpable axillary lymph nodes. Sonography showed a hypoechogenic mass with a 7.5-cm diameter, well-defined borders, and sporadic cyst areas in the periphery. Mammography showed an increased density at the inferior quadrants without calcifications (Figure 1). Core-needle biopsy revealed a benign feature: pseudoangiomatous stromal hyperplasia. Clinical follow-up was recommended. After 10 months, the patient experienced a significant increase in the size of the mass without other associated symptoms. Magnetic resonance imaging was performed. The images confirmed the presence of a well-encapsulated lesion measuring 11 cm in diameter. On T1-weighted imaging, the mass was isointense to the muscle with a homogeneous signal along the mass. On T2-weighted imaging, the mass was isointense to the mammary parenchyma. Contrast-enhanced, fat-suppressed fast-spoiled gradient-recalled echo images revealed a type II time-signal intensity curve and an intense ring-enhancing mass with large arteries and veins going to the mass (Figure 2). Surgical excision was indicated.