Pseudosarcomatous stromal reaction in primary and metastatic urothelial carcinoma. A source of diagnostic difficulty

We report five urothelial carcinomas (one primary and four metastatic) with pseudosarcomatous stromal reaction. The exuberant stromal reaction led to a histologic misdiagnosis in three of the original small biopsy specimens. The differential diagnoses of primary spindle cell lesions of urinary tract include spindle cell carcinoma, carcinosarcoma, sarcoma, and benign pseudosarcomatous lesions. The distinction between those conditions and urothelial carcinomas with pseudosarcomatous stromal reaction is obviously of great clinical significance. In an initial small biopsy specimen, it may be difficult to make such a distinction. Immunostaining for cytokeratin and examination of more material should be performed. In our study of metastatic urothelial carcinomas with pseudosarcomatous stromal reaction, clinicopathologic correlations along with immunostaining for keratin proved to be useful. The stromal inductive capability of transplanted urothelium, which has been established in animal experiments, has occasionally also been reported in humans. The malignant urothelium in humans similarly appears to be capable of inducing stromal reaction.