A 66-year-old woman with neuroendocrine carcinoma in situ (NE-DCIS) cytologically examined for a nipple discharge was found to have small to moderate irregular cells with a low N/C ratio and mild hyperchromatism against a hemorrhagic background. Immunocytochemistry showed tumor cells to be positive for synaptophysin. Histologically, round, uniform tumor cells with eosinophilic cytoplasm were arranged in a solid papillary pattern within the duct. Tumor cells contained vascular networks and were immunohistochemically positive for synaptophysin and chromogranin A, yielding a definitive diagnosis of NE-DCIS. The small to moderate irregular cells with their low N/C ratio and mild hyperchromatism with hemorrhage and positive immunocytological staining enabled preoperative diagnosis.
