Review Question - QID 108754

A 62-year-old female presents for a routine yearly mammogram. She denies breast discomfort, skin changes, or lumps on palpation. She has a past medical history significant for hyperlipidemia and hypertension. Her medications include simvastatin and hydrochlorothiazide. The patient has a family history of breast cancer in her maternal aunt at age 64 and type 2 diabetes mellitus in her father. Her temperature is 98.6°F (37°C), blood pressure is 132/71 mmHg, pulse is 91/min, and respirations are 12/min. A lesion is seen on a mammogram as shown in Figure A. A lesion biopsy is obtained and sent for pathology, confirming invasive ductal carcinoma with HER2/neu overexpression. A lumpectomy with sentinel lymph node biopsy is subsequently performed with negative margins and nodes. Which test should be performed before this patient receives the first-line chemotherapy agent for her diagnosis?