Cytomorphology of high-grade neuroendocrine carcinoma of the urinary tract.

High-grade neuroendocrine carcinoma of the bladder is a rare malignant tumor with poor prognosis. We present the cytomorphologic features of six retrospectively identified cases which displayed high-grade tumors with neuroendocrine differentiation in bladder washings. Cytology specimens showed small-to-medium-sized tumor cells with powdery chromatin, inconspicuous nucleoli, and ill-defined nuclear membranes. Tumor fragments showed prominent nuclear molding and single-cell necrosis. All cases also revealed a varying proportion of tumor cells resembling the usual transitional-cell carcinoma. Biopsy specimens from five cases demonstrated high-grade transitional-cell carcinoma with areas resembling small-cell carcinoma. In one case the entire tumor consisted of classic small-cell carcinoma and failed to show any areas of transitional-cell differentiation. All cases were positive for neuroendocrine markers. Neuroendocrine carcinomas of the urinary bladder are rare, with cytological features similar to high-grade neuroendocrine carcinomas seen in other organs. They can be accurately diagnosed cytologically, and an awareness of the cytomorphologic features is important.