Neuroendocrine Neoplasms of the Breast: Evolving Concepts and Reappraisal of Classification

Breast cancer encompasses a broad spectrum of differentiation patterns, some of which are associated with distinct clinical behaviors and therapeutic responses. Among these, tumors demonstrating neuroendocrine (NE) differentiation represent a histologically heterogeneous group that poses unique diagnostic and classification challenges. This group includes recognized tumor types with NE features, such as solid papillary carcinoma and hypercellular (type B) mucinous carcinoma, as well as invasive breast carcinoma of no special type with NE pattern. In addition, rare primary breast tumors classified as neuroendocrine neoplasms (NENs) have also been described. Ultimately, this article aims to clarify the pathological evaluation of breast NENs.