Signet ring cell carcinoma in urine cytology: Cytomorphologic findings and differential diagnosis

Background: Signet ring carcinoma is an exceedingly rare and aggressive variant of primary bladder carcinoma. The cytomorphologic features of this rare entity in urinary specimens have not been well characterized. Methods: Twenty-seven cases of signet ring cell carcinoma of the urinary bladder were identified from the pathology archives of The Johns Hopkins Hospital (1989-2011). Of these, 6 cases with prior urinary cytology specimens were studied. Results: There were 5 males and 1 female, with a mean age of 62 years. The presenting complaints included hematuria with or without symptoms of bladder irritation. Histopathologically, there were 5 cases of primary bladder carcinoma and 1 case of metastatic colonic signet ring cell carcinoma. The salient cytomorphologic features included scattered malignant epithelial cells, displaying distinct cell borders, abundant cytoplasm with a single large, discrete mucin vacuole, and eccentric irregular nuclei with prominent nucleoli. Primary adenocarcinoma additionally revealed a few intact malignant glandular epithelial fragments. Metastatic colonic signet ring cell carcinoma displayed predominantly singly dispersed malignant cells with eccentrically placed, oval nuclei with occasional small nucleoli and a moderate amount of vacuolated cytoplasm. Conclusion: Signet ring cell carcinomas are rarely encountered in urinary cytology. The differential diagnosis includes distended histiocytes or degenerated urothelial cells, primary signet ring cell carcinoma, and metastatic adenocarcinoma.