Bilateral Breast Metastases from Epstein-Barr Virus-Associated Gastric Cancer during Pregnancy: Is There a Method to Its Madness?

Breast metastases of extramammary malignant neoplasms are rare, with an incidence of 0.3%-2.7% among all malignant mammary tumors. Breast metastases from gastric carcinoma are very rare (<0.1%), and this event is even rarer during pregnancy. Herein, we describe a 39-year-old Caucasian woman with a history of an Epstein-Barr virus-associated gastric carcinoma (EBVaGC) that was characterized by prominent tumor infiltrating lymphocytes. Three years after undergoing radical surgery, the patient developed bilateral breast nodules during her pregnancy. A breast biopsy was performed, and histology confirmed a diagnosis of EBVaGC; tumor cells showed positivity for cytokeratin 8/18 and E-cadherin, and negativity for cytokeratin 7, cytokeratin 20, cytokeratin 5/6, caudal type homebox 2, androgen receptor, mammaglobin, gross cystic disease fluid protein-15, and estrogen and progesterone receptors. We also discuss the main diagnostic pitfalls. To our knowledge, this is the first report of an EBVaGC with lymphoid stroma that developed breast metastases during pregnancy.