Review Question - QID 215104

A 28-year-old G2P1 woman at 37 weeks' gestation presents to the clinic complaining of a new breast mass. The patient reports that she was showering yesterday when she felt a new lump in her left breast. She denies any discharge, fever, or recent trauma to the area but admits to being in a car accident 2 years ago. She denies any family history of breast cancer. She reports that she now feels lethargic and cold. She has no other significant past medical history and takes no medications. Her temperature is 97.0°F (36.1°C), blood pressure is 115/78 mmHg, pulse is 55/min, and respirations are 12/min. A chaperoned physical examination is notable for a periareolar, mobile, well-circumscribed, and nontender mass at the left breast. There are no overlying skin changes. An ultrasound study is performed, and its findings are shown in Figure A. Which of the following is the most likely diagnosis?