Fine-needle sampling of a case of carcinoma of the breast with neuroendocrine differentiation.

Fine-needle sampling was performed in a woman with a left breast lump. The cytologic diagnosis was consistent with a poorly-differentiated carcinoma. Cytologic features included medium-to-large, round, and spindle-shaped cells with scanty cytoplasm, nuclear molding, and rosette-like structures. Histology revealed an endocrine pattern. Immunohistochemical staining was positive for epithelial and neuroendocrine markers, and electron microscopy showed many small membrane-bound electron-dense granules, confirming the diagnosis of breast carcinoma with neuroendocrine differentiation. DNA flow cytometry and cytogenetic analyses revealed a near-tetraploid tumor.