A Rare Breast Tumor Confused with Ductal Carcinoma in Situ, Primary Solid Neuroendocrine Carcinoma.

The concept of pure neuroendocrine breast tumors was initially defined by Sapino et al. There are three sub-types of these tumors: solid, small cell/oat cell, and large cell neuroendocrine carcinomas. To diagnose neuroendocrine tumors, more than half of the tumor cells must have neuroendocrine differentiation. The possibility of metastatic neuroendocrine carcinoma must always be excluded in the differential diagnosis. In addition, it should be considered that solid neuroendocrine (NE) carcinomas can be confused with ductal carcinoma in situ due to their similar morphologic appearance. In this article, a patient with primary solid neuroendocrine breast cancer who had been diagnosed with ductal carcinoma in situ at another center was presented along with morphological and immunohistochemical features.