Clear cell adenocarcinoma of the lower urinary tract: cytopathologic characteristics and differential diagnoses.

Clear cell adenocarcinomas (CCAs) of the lower urinary tract are uncommon neoplasms that may present in routinely processed urinary cytology specimens. There is only limited discussion of the features of CCA of the lower urinary tract in the cytology literature. The authors report a series of 3 cases of this unusual tumor, and correlate cytomorphology with histologic specimens. Two of the cases were diagnosed accurately as adenocarcinoma, and 1 case was diagnosed as atypical cells of undetermined significance. Cytomorphologic features included variably cellular samples with 3-dimensional fragments of malignant cells that had enlarged nuclei, prominent nucleoli, and occasional hobnail configurations. Some fragments showed luminal formation with collections of neutrophils. CCA must be included in the differential diagnosis of malignant cells in a urinary specimen, particularly if the features are not typical of urothelial carcinoma. Other diagnostic considerations include metastatic adenocarcinomas, nephrogenic adenomas, and benign glandular lesions involving the bladder and urinary tract such as mullerianosis.