What Is the Significance of Variant Histology in Urothelial Carcinoma?

CONTEXT: Urothelial carcinoma can exhibit a wide range of variant morphologies. Many variants present diagnostic challenges and carry clinical implications that inform prognosis and treatment decisions. OBJECTIVE: To provide an overview of the diagnostic, therapeutic, and prognostic significance of histological variants of urothelial carcinoma. EVIDENCE ACQUISITION: A PubMed/MEDLINE-based literature search was conducted using the key terms "urothelial carcinoma", "variant histology", "nested", "micropapillary", "microcystic", "sarcomatoid", "squamous differentiation", "glandular differentiation", "clear cell", "plasmacytoid", "lymphoepithelioma-like carcinoma", "squamous cell carcinoma", "small cell carcinoma", "adenocarcinoma", "radiotherapy", "neoadjuvant chemotherapy", and "adjuvant chemotherapy". EVIDENCE SYNTHESIS: The incidence of variant histology is increasing due to improved recognition. Nonetheless, diagnosis can pose challenges due to sampling limitations and interobserver variability. Although associated with advanced disease at presentation, survival outcomes for most variants do not differ significantly compared with pure urothelial carcinoma of the same stage. Controversy exists regarding optimal management due to the low quality of available evidence. For most cases, radical cystectomy with pelvic lymph node dissection (with neoadjuvant chemotherapy when appropriate) represents the standard of care. Small cell carcinoma and lymphoepithelioma-like carcinoma appear to be particularly chemosensitive. CONCLUSIONS: Accurate identification of variant histological subtypes is an important part of risk stratification, as these variants exhibit aggressive biological behaviour. Variant histology tumours are associated with advanced disease at presentation, which must be considered when counselling patients regarding survival outcomes. Optimal management remains to be defined but in most cases; neoadjuvant chemotherapy and radical cystectomy with pelvic lymph node dissection remains the mainstay of treatment. PATIENT SUMMARY: It is important to recognise histological variants of urothelial carcinoma as they indicate aggressive disease. When compared with patients with pure urothelial carcinoma of the same disease stage, survival does not appear to be significantly worse. In most cases, patients with invasive variant histology should be treated with neoadjuvant chemotherapy and radical cystectomy. Take Home Messages Accurate identification of variant histology is important as it exhibits aggressive biological behaviour and affects treatment. Although associated with advanced disease at presentation, with appropriate treatment, survival outcomes are not significantly different compared with pure urothelial carcinoma of the same stage.

Gene Expression Profile of the Clinically Aggressive Micropapillary Variant of Bladder Cancer.

BACKGROUND: Progression of conventional urothelial carcinoma of the bladder to a tumor with unique microscopic features referred to as micropapillary carcinoma is coupled with aggressive clinical behavior signified by a high propensity for metastasis to regional lymph nodes and distant organs resulting in shorter survival. OBJECTIVE: To analyze the expression profile of micropapillary cancer and define its molecular features relevant to clinical behavior. DESIGN, SETTING, AND PARTICIPANTS: We retrospectively identified 43 patients with micropapillary bladder cancers and a reference set of 89 patients with conventional urothelial carcinomas and performed whole-genome expression messenger RNA profiling. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: The tumors were segregated into distinct groups according to hierarchical clustering analyses. They were also classified according to luminal, p53-like, and basal categories using a previously described algorithm. We applied Ingenuity Pathway Analysis software (Qiagen, Redwood City, CA, USA) and gene set enrichment analysis for pathway analyses. Cox proportional hazards models and Kaplan-Meier methods were used to assess the relationship between survival and molecular subtypes. The expression profile of micropapillary cancer was validated for selected markers by immunohistochemistry on parallel tissue microarrays. RESULTS AND LIMITATIONS: We show that the striking features of micropapillary cancer are downregulation of miR-296 and activation of chromatin-remodeling complex RUVBL1. In contrast to conventional urothelial carcinomas that based on their expression can be equally divided into luminal and basal subtypes, micropapillary cancer is almost exclusively luminal, displaying enrichment of active peroxisome proliferator-activated receptor γ and suppression of p63 target genes. As with conventional luminal urothelial carcinomas, a subset of micropapillary cancers exhibit activation of wild-type p53 downstream genes and represent the most aggressive molecular subtype of the disease with the shortest survival. The involvement of miR-296 and RUVBL1 in the development of micropapillary bladder cancer was identified by the analyses of correlative associations of genome expression profiles and requires mechanistic validation. CONCLUSIONS: Micropapillary cancer evolves through the luminal pathway and is characterized by the activation of miR-296 and RUVBL1 target genes. PATIENT SUMMARY: Our observations have important implications for prognosis and for possible future development of more effective therapies for micropapillary bladder cancer.