A Case of Cytokeratin 20-positive Large-cell Neuroendocrine Carcinoma of the Breast

We report a rare case of large-cell neuroendocrine carcinoma of the breast. A 63-year-old woman was admitted to our hospital with a firm mass in the right breast. Mammography revealed a high-density mass with specula, and ultrasonography showed a heterogeneous hypoechoic mass with irregular margin and posterior acoustical shadowing. She underwent breast-conserving surgery with axillary lymph node dissection. Histopathologically, the tumor consisted of large cells with polygonal and prominent nuclei and a small amount of eosinophilic cytoplasm, and these cells showed palisading arrangement with fibrous stroma. The tumor cells were positive for neuroendocrine markers such as NSE, synaptophysin, CD56 (NCAM), but not for chromogranin A. Interestingly, the tumor cells showed reactivity for cytokeratin 20 but not for cytokeratin 7. The immunostaining pattern is different from the usual adenocarcinoma of the breast. The patient received postoperative radiotherapy and was given adjuvant chemotherapy. She has remained disease-free for 44 months.