Non-Urothelial Malignancy in Urine Cytology

Abstract

Non-urothelial malignancies of the urinary bladder are relatively rare and can be classified into primary and secondary malignancies. The histological subtypes of non-urothelial malignancy include non-urothelial carcinoma, sarcoma, lymphoma, and melanoma. The common types of primary non-urothelial carcinoma are pure squamous cell carcinoma, adenocarcinoma, and small cell carcinoma. Most primary sarcomas of the urinary bladder are leiomyosarcoma and rhabdomyosarcoma. Extranodal marginal zone B-cell lymphomas of mucosa-associated lymphoid tissue origin and diffuse large B-cell lymphoma (DLBCL) are the common primary lymphomas of the urinary bladder. Most secondary tumors of the urinary bladder result from the direct extension of adjacent organs such as the colon/rectum, prostate, and cervix. Hematogenous metastasis from other primary cancers such as breast, stomach, lung, and skin (melanoma) are less common. The cytologic diagnosis of non-urothelial malignancies is challenging due to the significant cytomorphologic overlap with high-grade urothelial carcinoma, its divergent differentiation, and subtypes. Awareness of these diagnostic entities is helpful for accurate diagnosis, especially when encountering urine specimens with unusual cytomorphology.