Micropapillary Carcinoma of the Bladder: Recent Advances

Abstract

The 2016 WHO classification of tumors of the urothelial tract recently revised the classification of invasive urothelial carcinoma to include nested, microcystic, micropapillary, plasmacytoid, sarcomatoid, giant cell, and poorly differentiated variants, among others. In particular, invasive micropapillary carcinoma (IMPC) is now recognized as a distinct entity with aggressive features, including higher-stage disease, invasive features, and poorer response to intravesical chemotherapy. In this review, we highlight recent studies that further characterize the histopathology, immunohistochemistry, molecular mechanisms, and clinical implications of a diagnosis of IMPC. Because the correct morphologic diagnosis of IMPC is critical in terms of clinical management, we explore the diagnostic criteria of IMPC and differential diagnosis of urothelial IMPC from non-urothelial sites, highlighting studies that examine both traditional urothelial immunohistochemical markers as well as novel markers. We highlight recent advances in the molecular sub-categorization of IMPC, and review the differences compared to other forms of urothelial carcinoma. Optimal management of patients with IMPC is still unclear, although early cystectomy, regardless of pathologic stages, is recommended. We also highlight several studies that address the clinical challenges as well as current treatment protocols for IMPC.