Histogenesis of clear cell adenocarcinoma in the urinary tract: evidence of urothelial origin.

PURPOSE Clear cell adenocarcinoma in the urinary tract is a rare entity with an appearance resembling its counterpart in the female genital tract. Although several theories have been proposed about its origin, its exact histogenesis has remained uncertain. EXPERIMENTAL DESIGN We integrated molecular genetic evaluation by fluorescence in situ hybridization and X-chromosome inactivation with conventional morphologic and immunohistochemical analyses in 12 patients with clear cell adenocarcinomas in the urinary tract. RESULTS Concurrent urothelial carcinoma or urothelial carcinoma in situ was present in six cases (50%) and foci of cystitis glandularis were observed in four cases (33%). Neither intestinal metaplasia nor Müllerian component was identified in any case. Cytoplasmic expression of alpha-methylacyl-CoA racemase was demonstrable in 10 of 12 tumors (83%). Moderate to diffuse immunostaining for cytokeratin 7 was identified in all 12 tumors (100%), whereas only 3 of 12 (25%) tumors showed positive immunostaining for cytokeratin 20. Focal uroplakin III staining was seen in 6 of 12 tumors (50%). In five cases (42%), focal to moderate CD10 immunoreactivity was observed. Immunostains for OCT4 and CDX2 were completely negative in all tumors. In UroVysion fluorescence in situ hybridization assays, all tumors displayed chromosomal alterations similar to those commonly found in urothelial carcinoma. Identical patterns of nonrandom X-chromosome inactivation in concurrent clear cell adenocarcinoma and urothelial neoplasia were identified in two informative female cases. CONCLUSIONS Our findings support an urothelial origin for most clear cell adenocarcinomas of the urinary tract, despite their morphologic resemblance to certain Müllerian-derived tumors of the female genital tract.