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Neuroendocrine neoplasms (NEN) of the breast are specific tumor entities. According to the literature up to 5% of breast neoplasms are malignant epithelial neoplasms of the breast. They are defined by a neuroendocrine (NE) architecture and cytology combined with an expression of the neuroendocrine vesicle markers chromogranin A and/or synaptophysin. The diagnosis is supplemented by the receptor status and the proliferative activity. According to the World Health Organization (WHO) classification of 2012 the following groups of NEN are distinguished: (1) invasive breast carcinoma with NE differentiation, (2) well-differentiated neuroendocrine tumor (NET) and (3) poorly differentiated small cell carcinoma (NEC). This review article focuses on (1) the definition and basic principles of diagnostics, (2) the history, nomenclature and WHO classification from 2003 and 2012, (3) the frequency of breast NEN, (4) the hereditary background and functional activity, (5) the expression of receptors and (6) the possible clinical implications. In addition, the first results of a retrospective single center study (n = 465 patients with breast cancer over a time period of 4 years) on the frequency of NEN of the breast at the Breast Center of the University Hospital Düsseldorf are presented. In this study a frequency of 4.5% of NEN was found based on a diagnostic cut-off of > 50% Chromogranin A and/or synaptophysin positive tumor cells.

Neuroendocrine neoplasms (NEN) of the distal jejunum and ileum derive from serotonin-producing enterochromaffin (EC) cells. Due to their low proliferation rate and their infiltrative growth, they are often discovered at an advanced disease stage when metastasis has already occurred. The biology of these tumours is different from other NEN of the digestive tract. In order to standardise and improve diagnosis and therapy, the guidelines for the diagnosis and clinical management of jejuno-ileal NEN as well as for the management of patients with liver and other distant metastases from NEN were revised by the European Neuroendocrine Tumour Society (ENETS) in 2012. This review focuses on aspects relevant for surgical pathology.

Breast cancer metastases to the head and neck region are very rare and therefore represent a challenge for the clinician in terms of diagnosis and therapy. Recent advances in breast cancer treatment have achieved longer median survival times in affected patients. However, at the same time, the risk of a clinical manifestation of metastasis increases. Here we present the cases of two breast cancer patients who developed filiae into the petrous portion of the temporal bone and one very rare case of metastasis to the larynx. Diagnosis, therapy and distinctive features of metastasis to the head and neck region are discussed.Secondary to long-term endocrine hormone therapy, a reduction in estrogen receptor expression occurred in all three cases. We believe that the loss of steroid receptor expression contributed to tumor resistance to endocrine therapy. Moreover, this receptor loss hindered the pathologist from confirming the diagnosis of metastases at very unusual sites.