Breast Carcinoma With Unrecognized Neuroendocrine Differentiation Metastasizing to the Pancreas

The current World Health Organization classification recognizes 3 subtypes of breast carcinomas with neuroendocrine features. Their reported prevalence is highly variable, ranging from <1% to up to 20% of all breast carcinomas. We report the case of a 73-year-old woman who underwent lumpectomy with a postoperative diagnosis of invasive ductal breast carcinoma. Six weeks after lumpectomy, pancreatic biopsies showed tumor cells with neuroendocrine features. The first immunohistochemical panel showed positivity for synaptophysin and cytokeratins, raising suspicion of a pancreatic neuroendocrine tumor. However, a second panel revealed positivity for estrogen receptors and GATA3. On review of the lumpectomy specimen, a significant neuroendocrine component was found, leading to the final diagnosis of breast carcinoma with neuroendocrine features metastasizing to the pancreas. Neuroendocrine markers are not routinely analyzed in breast tumors. Hence, metastases from breast carcinomas with unrecognized neuroendocrine features may lead to false diagnoses of primary neuroendocrine tumors at different metastatic sites, such as the pancreas.