[Invasive breast carcinoma with features of neuroendocrine carcinoma and carcinoma with osteoclastic cells: fine-needle aspiration cytology and histology of two cases].

We report two cases, with overlapping cyto-histological characteristics, of invasive neuroendocrine carcinoma of the breast with associated stromal features distinctive of carcinoma with osteoclastic giant cells. Fine-needle aspiration cytology showed monomorphic, medium-sized, mildly atypical neoplastic cells, with interspersed multinucleated giant cells and lympho-histiocytic components; hemosiderin deposits were also appreciable. Macroscopic features were typical of invasive carcinoma, but with unusual brown staining. Light microscopy revealed moderately differentiated invasive carcinoma mainly composed of solid sheets of round to polygonal medium-sized cells with a tendency to produce peripheral palisading (carcinoid-like morphology); osteoclast-like multinucleated giant cells, lymphocytes and histiocytes were dispersed only among tumour cells in the distinctive stroma of the carcinoma with osteoclastic giant cells; this stroma was characterised by reactive/fibroblastic features, hypervascularization, extravasated blood cells and hemosiderin deposits that gave rise to the typical staining seen macroscopically. Immunohistochemically, cancer cells were diffusely positive for the neuroendocrine marker synaptophisin with partial chromogranin and NSE staining; the ostoclastic giant cell and histiocyte component were strongly positive for CD68. Both cases also had lymph node metastases; the epithelial neoplastic cells, with regards to neuroendocrine markers, were overlapping to the primitive tumour, the histiocytic/giant cell component appeared present, although with a lower degree, while the distinctive stroma was absent. Breast neuroendocrine carcinomas, associated with multinucleated giant cells and stroma typical of the carcinoma with osteoclastic-like cells, to our knowledge, have not been reported.