A 35-year-old woman presented to her primary care physician for evaluation of a palpable left breast mass. Diagnostic mammography revealed 2 separate masses: a 1.4-cm mass at the 3 o’clock position, 10 cm from the nipple; and a 1.3-cm mass in the lateral breast, 4 cm from the nipple. Ultrasound of the axilla revealed an enlarged lymph node found to be malignant on fine-needle aspiration cytology. Image-guided core biopsies of both masses revealed a poorly differentiated invasive ductal adenocarcinoma. Estrogen receptor (ER) was strongly positive in 95% of tumor cells, progesterone receptor (PR) was positive in less than 5% of tumor cells, and human epidermal growth factor receptor 2 (ERBB2 [HER2]) by immunohistochemistry (IHC) was scored as 1+ (Table).
Hilal T, Romond EH. ERBB2 (HER2) Testing in Breast Cancer. JAMA. 2016;315(12):1280-1281. doi:10.1001/jama.2015.17463