High-grade urothelial carcinoma of the urinary bladder showing acquisition of microcystic histology in the penile metastasis: histogenetic considerations.

Microcystic urothelial carcinoma is a rare variant of transitional cell carcinoma with an indefinite prognostic significance. Herein, we report for the first time the acquisition of microcystic histology in the penile metastasis of a high-grade urothelial carcinoma of the urinary bladder. The patient died of disseminated disease six months later. The immunohistochemical evaluation of mucin expression in the primitive and metastatic tumor suggests that the microcystic histotype may descend from the primitive urothelial carcinoma through a process of dedifferentiation and subsequent redifferentiation. In conclusion, the acquisition of microcystic histology seems to be associated with an aggressive clinical course of the urothelial carcinoma, as already suggested by other authors. Future studies investigating mucin expression in microcystic urothelial carcinoma may help to define the histogenesis of this tumor.