Neuroendocrine breast carcinomas (NEBC) are rarely malignant with a frequency of less than 0.1-0.3% of all breast tumors. The actual incidence of NEBC in BC (Breast Cancer) populations being still largely unknown due to the lack of a clear cut diagnostic criteria. In 2003, the World Health Organization (WHO) Classification of Tumors of the Breast and Female Genital Organs definitely established that the immunohistochemical expression of NE markers is the unique requirement for NEBC diagnosis [1] in more than 50% of the tumor cell population. In the 2012 WHO Classification of the Tumors of the Breast these entities were collected in another chapter, among the special sub-types: Carcinomas with neuroendocrine features, which encompass the categories of Neuroendocrine tumors which are well differentiated, Neuroendocrine carcinoma which is a poorly differentiated/small cell carcinoma and Invasive breast carcinoma with neuroendocrine differentiation.

We would like to report the case of a 67-year-old woman with a rare neuroendocrine well differentiated breast cancer detected accidentally during a PET performed as a follow up in the treatment of a bone plasmacitoma. The result of histological examination was well differentiated primary neuroendocrine tumor of the breast with CKPan+, SYn+; CK7- and CK5-; ER+, Pr+, HER2- and ki67 < 5% [1].

The prognosis of NECB is not different from other invasive breast carcinomas and the most important prognostic factor is the tumor grade (G). However, there is no standard treatment and patients should be treated similarly to patients with invasive ductal carcinoma, NOS (Not Otherwise Specified), the choice of therapy depending on the size of the tumor, the degree of differentiation, the clinical stage, and the hormonal status.