Talal Hilal, MD; Edward H. Romond, MD

Diagnostic mammography revealed 2 masses in the left breast of a 35-year-old woman. Image-guided core biopsies revealed a poorly differentiated invasive ductal adenocarcinoma. Estrogen receptor was strongly positive in 95% of tumor cells, progesterone receptor was positive in less than 5% of tumor cells, and ERBB2 (HER2) by immunohistochemistry was scored at 1+. How do you interpret the test results?

JAMA