Small-cell undifferentiated carcinoma (SCUC) has been increasingly recognized in the urinary tract. 1,2,3 Up to 66% of SCUCs in this location are associated with a minor component of a more differentiated carcinoma that most frequently represents transi tional-cell carcinoma (TCC), but adenocarcinoma, squamous-cell carcinoma, spindle- cell carcinoma, and carcinoid carcinoma have all been described. We report a case of low-grade TCC of the urinary tract metastasizing to a distant location and therein dedifferentiating into an SCUC and discuss the clinical and biologic implication of the process of dedifferentiation. Int J Surg Pathol 2(2):157-162, 1994
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