Inflammatory breast cancer Quiz: Ace Your Exams

A 42-year old woman presents to the primary care office after being treated in urgent care for breast pain one week ago. She is on day seven of antibiotics for presumed mastitis and has not had improvement in the redness or swelling of her right breast. She has not had fevers, chills, or night sweats. Family history includes breast cancer in her mother at age 46. Temperature is 37.0°C (98.6°F), pulse is 82/min, respiratory rate is 18/min, and blood pressure is 124/82 mmHg. Chaperoned exam reveals edema, warmth, and tenderness over the medial and inferior portions of the right breast. The area is firm to palpation without fluctuance. Skin changes can be seen in the image below. Ultrasound shows thickening and edema of the skin without an underlying fluid collection or mass.  Which of the following tests will confirm the underlying diagnosis?
 
^{Image by Levine PH, Zolfaghari L, Young H, Hafi M, Cannon T, Ganesan C, Veneroso C, Brem R, Sherman M - Cancers (2010), cropped from original, is licensed under CC BY 3.0 DEED.  Reproduced from Open-i.}