Fine needle aspiration cytology of a male breast carcinoma exhibiting neuroendocrine differentiation. Report of a case with immunohistochemical, flow cytometric and ultrastructural analysis.

We present the cytologic, immunohistochemical, flow cytometric and ultrastructural findings of a case of invasive ductal carcinoma of the breast with features of neuroendocrine differentiation occurring in an 83-year-old male. Fine needle aspiration (FNA) cytology of the patient's tumor demonstrated a markedly cellular specimen to discohesive tumor cells, present primarily singly, with occasional loose groups. The cells were relatively large, with pleomorphic, eccentrically placed, round to oval nuclei. The cytoplasm was abundant and contained prominent red granules (Papanicolaou stain) that were also argyrophilic. Immunohistochemical studies performed on the aspirate and the subsequently excised malignant breast tissue revealed positive staining for neuron-specific enolase, chromogranin A, synaptophysin and gastrin. Also, the majority of the tumor stained positive with antibodies to both estrogen and progesterone hormone receptors. DNA flow cytometry demonstrated an aneuploid stemline population with a DNA index of 1.73 and an S-phase fraction of 4.5%. Electron microscopy was performed on the FNA material, and numerous variable-sized, membrane-bound, dense-core granules diffusely scattered within the cytoplasm of the neoplastic cells were identified. The specific cytologic features of this tumor, along with the immunocytochemical and ultrastructural features, can aid the pathologist in rendering an accurate FNA diagnosis of this specific subtype of breast carcinoma.