Transition between urothelial carcinoma in situ and non-invasive micropapillary carcinoma as a pivot connection between diverse morphologies of bladder carcinoma: a case report of urothelial carcinoma with villoglandular differentiation.

Urothelial carcinoma has numerous histological variants, and these variants may coexist in a single case. Here, we present a case of a 70-year-old man with urothelial carcinoma of the bladder with a maximal diameter of 5 mm that involved micropapillary and plasmacytoid variants, with villoglandular differentiation. The presence of these variants was confirmed by pathological examination of a transurethral resection specimen, and high-grade urothelial carcinoma was found as a minor component. Although this bladder carcinoma was classified as pT1, cystoprostatectomy, urethrectomy, and lymphadenectomy were performed due to the presence of the micropapillary and plasmacytoid variants, which are known to be aggressive. Examination of a surgically resected specimen revealed no carcinoma. A transition between urothelial carcinoma in situ and non-invasive micropapillary carcinoma was found to be a pivot point connecting the diverse morphologies of this bladder carcinoma, from which there existed two pathways. One pathway was from urothelial carcinoma in situ to the plasmacytoid variant through invasive high-grade urothelial carcinoma, and the other was from non-invasive micropapillary carcinoma to urothelial carcinoma with villoglandular differentiation or to the micropapillary variant. This is the 16th reported case of urothelial carcinoma with villoglandular differentiation in the literature. As urothelial carcinoma with villoglandular differentiation is often associated with aggressive variants, as shown in our case, it should be reported whenever encountered in routine pathological practice.