A case of solid neuroendocrine carcinoma of the breast in a 40-year-old woman.

We report a case of neuroendocrine carcinoma in a 40-year-old woman who presented with two lumps in her left breast. Mammography failed to reveal any lesions because she had so-called dense breasts, but ultrasonography showed 4 irregular hypoechoic masses. Magnetic resonance imaging also showed 4 homogeneous lobulated tumors with early contrast enhancement, suggesting malignancy. Core needle biopsy and subsequent immunohistochemical examination of the specimens was performed. Neuroendocrine carcinoma was diagnosed. The tumor cells were diffusely positive for chromogranin A and synaptophysin, and some were positive for CD56. We performed total mastectomy with sentinel lymph node biopsy, which showed no metastasis. Recurrence has not been detected at 36 months after surgery.