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Some primary carcinomas of the breast have been classified as neuroendocrine. In this paper we report on 12 cases of neuroendocrine carcinoma of the breast displaying common and uncommon histological features. Materials and methods: All patients were aged from 43 to 79 (median 66.5) years. The tumors were unilateral and ranged from 0.8 to 7 cm (median 2.35 cm) in diameter. Four tumors were classified as solid cohesive, two as solid papillary, one as Merkel cell-like, two as cellular mucinous, two as cellular mucinous with micropapillary features and one as cellular mucinous with prominent signet ring cells. The tissues were fixed in formalin and routinely processed. All materials were stained with PAS, Alcian blue and also hematoxylin and eosin. Immunohistochemical examination was carried out by the avidin-biotin method using the following antibodies: estrogen receptor protein, progesterone receptor protein, p53, cerbB-2, Ki67, neuron-specific enolase, chromogranin, and synaptophysin. Results: In all cases the tumor cells were stained positively with NSE. Synaptophysin and chromogranin positivity was detected in I I and five cases, respectively. The prominent histological features were: extensive intraductal growth, pseudorosettes and palisades, low-grade cytologic atypia, plasmacytoid appearance of the tumor cells, and intracellular and extracellular mucin. Conclusion: Neuroendocrine-differentiated carcinoma of the breast is a rare and distinct category with different histological subtypes. (C) 2003 Elsevier Science Ltd. All rights reserved.

Invasive micropapillary carcinoma of the breast is an uncommon variant of infiltrating ductal carcinoma. Observing its distinctive cytologic appearance and aggressive behavior is important for early diagnosis by fine-needle aspiration cytology (FNAC). There are only a few reported cases in the literature. Five women presented with breast masses. FNAC showed malignant epithelial tumors, and mastectomy materials showed invasive micropapillary carcinoma for all of them. Three patients had axillary lymph node metastases. Invasive micropapillary carcinoma, with its angulated papillary clusters lacking a fibrovascular core, and irregular crowded nuclei, has a distinctive cytologic appearance which correlates with its histological features. A differential diagnosis from other primary or metastatic papillary lesions of the breast may be possible using immunohistochemistry and some cytologic features. The limited experience with invasive micropapillary carcinoma should not discourage others from undetaking further studies. © 2002 Wiley-Liss, Inc.