Neuroendocrine Tumors of the Breast: Single-Center Experience.

Objective: Breast carcinomas with neuroendocrine (NE) differentiation are extremely rare. The aim was to discuss breast cancer cases with NE differentiation in the light of World Health Organization 2019 classification and literature information.

Material and methods: The pathology records of 56 cases diagnosed as neuroendocrine tumor (NET) and/or breast cancers with NE differentiation presenting to a single center between January 2010 and June 2020 were evaluated. The patients were evaluated in terms of age, tumor size, location, histological grade, hormone profiles (ER, PR, HER2), guideline American Joint Committee on Cancer, lymph node status, stage, metastases, progression, survival, radiological features, surgery type and therapy modality.

Results: The age of the patients ranged from 34 to 81 years. Average tumor size was 2.3 cm. Median (range) follow up time was 31.5 (1-73 month). Metastatic lymph nodes were found in 20 cases. In our series, NE differentiation mostly accompanied invasive carcinoma of no special type, less frequently solid papillary carcinoma, and mucinous carcinoma.Four patients had a history of neoadjuvant chemotherapy. Response to treatment was very poor in all four cases. Synaptophysin and chromogranin were positive in 38 cases. No correlation was found among tumor size, grade, age, lymph node status, and presence of distant metastasis in our series.

Conclusion: Clinical features and morphology may not help to distinguish NET from other subtypes of breast cancer. Therefore, the morphologic findings of a nested or trabecular architecture, nuclear or cytoplasmic features of NE differentiation, mucin production, or solid papillary growth pattern should prompt a pathologist to order NE markers.