Rare Human Epidermal Growth Factor Receptor 2 (HER-2)-Positive Neuroendocrine Carcinoma of the Breast: A Case Report with 9-Year Follow-up

Objective: Rare disease Background: Neuroendocrine carcinoma of the breast (NECB) is very rare, accounting for 0.1% of all breast tumors and less than 1% of all neuroendocrine tumors. Most NECBs are hormone receptor-positive and human epidermal growth factor receptor 2 (HER-2)-negative and more than 50% are the luminal B subtype. Because prospective studies of NECB are lacking, treatment is the same as for other breast tumors. Case Report: A 70-year-old woman was diagnosed with NECB in February 2011. She underwent radical right mastectomy and right axillary node dissection. Final histopathological examination revealed NECB with positive axillary nodes (N1). The tumor cells were 100% positive for estrogen receptors and 10% positive for progesterone receptors. The HER-2 status was 3+. According to the Tumor, Node, Metastasis (TNM) Classification of Malignant Tumors, the pathologic stage was IIB - pT2pN1cM0. The histologic grade was 2 and the Ki-67 proliferation index was 5.7%. The patient received adjuvant chemotherapy, radiation therapy, IV trastuzumab, and endocrine therapy. After 9 years of follow-up, she remains disease-free. Conclusions: As far as we know, this is only the second report describing treatment of HER-2-positive NECB with trastuzumab. A literature review shows that it is the first report of treatment of HER-2-positive primary NECB with adjuvant trastuzumab. In similar cases, long-term follow-up is recommended because of the potential for multiple metastases of NECB even years after completion of adjuvant therapy.