Histopathologic and biologic characteristics of a transitional cell carcinoma with inverted papilloma-like endophytic growth pattern.

To evaluate histopathologic and biologic characteristics in a patient with transitional cell carcinoma (TCC) with an endophytic growth pattern similar to that seen in an inverted papilloma. Although the tumor surface was mostly covered with normal-looking urothelium, the covering layer was thicker in parts than in those of benign papillomas. The widths of the trabeculae were irregular, and cytologic atypia with remarkable mitosis was seen. High expression of p53, Ki67, and cytoplasmic cyclin D1 was demonstrated by immunohistochemical staining. To clarify the biologic activities of tumors with inverted papilloma-like growth pattern, even when it appears as benign lesions by routine pathologic examination, analyses of immunoreactivity for proliferation markers might be critical.