Neuroendocrine tumors of the breast: Myth or reality? A systematic review

Primary neuroendocrine breast carcinomas are rare and little-known tumors. Only a limited number of studies on neuroendocrine breast carcinomas have been reported in the literature, and the vast majority of them are small retrospective series or case reports. According to the World Health Organization (WHO), they account for only 2 % to 5 % of breast cancers. Their diagnosis relies on the presence of a neuroendocrine architecture and the expression of neuroendocrine markers (chromogranin A and/or synaptophysin). The revised 2012 WHO classification subdivides them into three categories: (i) well-differentiated neuroendocrine carcinomas, (ii) poorly differentiated neuroendocrine carcinomas or small-cell carcinomas, and (iii) invasive breast carcinomas with neuroendocrine differentiation. Their clinical features and radiological characteristics are not different from those of other types of breast cancer. Because of discordant results, their clinical outcome is still poorly defined. So far, no standard treatment has been established, and most clinicians draw on their experience of invasive ductal cancer. The role of specific treatments like platinum-based chemotherapy, somatostatin analogues, peptide receptor radionucleide therapy or temozolomide remains unclear. A better knowledge of the molecular pathways involved in their carcinogenesis could help to identify new potential therapeutic targets. The efficacy of targeted therapies has to be studied.