Biomarkers to diagnose metastatic breast carcinoma to the pancreas: A case report and update.

The patient is a 72-year-old female who presents with new onset jaundice. The patient has a past medical history significant for right-sided estrogen receptor (ER)-positive and left-sided ER-negative breast cancers in 2005 and 2009, respectively, and recent 1-year history of ER-positive right-sided breast cancer with bone and brain metastases. CT scan and endoscopic ultrasound (EUS) revealed a new 2 cm mass in the head of the pancreas, leading to EUS-guided fine-needle aspiration of the lesion. Pathologic workup revealed adenocarcinoma with signet-ring cells, representing either metastatic breast or primary pancreatic cancer. Immunohistochemistry and molecular diagnostic workup identified positive GATA-binding protein 3 (GATA3) immunoreactivity and a mutation in Erb-B2 receptor tyrosine kinase 2 (ERBB2), also known as human epidermal growth factor receptor 2 (HER2). Here, we review the diagnostic markers commonly used to differentiate metastatic breast vs primary pancreatic adenocarcinoma, and discuss the challenges of utilizing GATA3 immunoreactivity and ERBB2 mutations for diagnosis.