Cloutier J, et al. - In the present study, researchers reported on a series of metastatic breast carcinoma (MBC) mimicking visceral well-differentiated neuroendocrine neoplasms. For this analysis, they identified five consultation cases originally submitted as neuroendocrine neoplasms in females, but which were found to be MBC on subsequent review. The study findings suggested that MBC with neuroendocrine differentiation should be considered in patients with visceral neuroendocrine neoplasms of an unknown primary site. They found that neuroendocrine differentiation was uncommon in breast cancer and did not commonly increase in metastases. They observed that immunohistochemistry for estrogen receptor (ER) and GATA3 could help establish the diagnosis.