Abstract
A 39-year-old man noticed a tumor in his left breast and underwent fine-needle aspiration cytology, which revealed cancer cells with rosettes. He underwent left mastectomy and dissection of the axial lymph nodes. Upon macroscopic examination, the tumor was observed to be 35 mm in size and located just under the nipple. Histopathological examination revealed that the tumor consisted of solid nests of uniform cells with invasion. Immunohistochemistry indicated neuroendocrine differentiation of the tumor due to high-level expression of synaptophysin and chromogranin. The expressions of estrogen receptors, progesterone receptors, human epidermal growth factor receptor 2, and the Ki-67 index were strongly present, strongly present, absent, and present in 5% or less of the tumor, respectively. No metastatic cells were found in the dissected axillary lymph nodes. We diagnosed this tumor as an invasive carcinoma with neuroendocrine differentiation. After receiving tamoxifen for 5 years, no recurrence was detected.
