Primary Small Cell Neuroendocrine Carcinoma of the Breast in a 75-Year-Old Woman With Aggressive Recurrence Despite Multimodal Therapy: A Case Report and Literature Review.

BACKGROUND Neuroendocrine breast tumors represent an uncommon subtype of breast cancer, accounting for less than 1% of all breast malignancies and fewer than 0.1% of all neuroendocrine tumors. Their histological and immunophenotypic features closely resemble neuroendocrine neoplasms of other organs, and diagnosis requires careful exclusion of extramammary primaries. CASE REPORT We present the case of a 75-year-old woman diagnosed with primary small cell neuroendocrine breast carcinoma following an incidental detection of a right breast mass. She underwent a simple mastectomy with sentinel lymph node biopsy, followed by adjuvant carboplatin-etoposide chemotherapy. One year later, she developed a solitary hepatic metastasis, which was successfully treated with metastasectomy and repeat adjuvant chemotherapy. Despite initial responses, subsequent surveillance imaging demonstrated progressive hepatic metastatic disease. This case underscores the aggressive clinical behavior and diagnostic challenges associated with high-grade neuroendocrine breast tumors. The 2019 WHO classification highlights the importance of distinguishing neuroendocrine carcinoma subtypes due to differing prognostic and therapeutic implications. Although multiple treatment modalities exist, outcomes remain poor in high-grade or advanced disease. CONCLUSIONS Neuroendocrine breast tumors remain insufficiently understood because of their rarity. This report highlights the importance of thorough histopathological evaluation, meticulous exclusion of extramammary primaries, and close longitudinal follow-up. Additional research is needed to establish standardized diagnostic and therapeutic guidelines.