Plasmacytoid urothelial carcinoma (UC) are luminal tumors with similar CD8+ Tcell density and PD-L1 protein expression on immune cells as compared to conventional UC

Molecular Subtypes of Bladder Cancer: Component Signatures and Potential Value in Clinical Decision-making

Bladder cancer may be classified into "molecular subtypes" based on gene expression. These are associated with treatment response and patient outcomes. The gene expression signatures that define these subtypes are diverse, including signatures of epithelial differentiation, stromal involvement, cell cycle activity, and immune cell infiltration. Multiple different systems are described. While earlier studies considered molecular subtypes to be intrinsic properties of cancer, recent data have shown molecular subtypes change as tumors progress and evolve, and often differ between histologically distinct regions of a tumor. The data also indicate that some signatures that define molecular subtypes may be treated as independent continuous variables, rather than categorical subtypes, and these individual signatures may be more clinically informative. This review describes molecular subtypes of urothelial carcinoma, including histologic subtypes and tumors with divergent differentiation, and explores potential future uses in patient management.

Molecular characterization of plasmacytoid urothelial carcinoma and the impact on treatment implications

Bladder cancer researchers and clinicians have increasingly viewed tumor biology through the lens of genomic and molecular alterations, drastically improving our knowledge of the underlying disease biology. This understanding has led to significant advances in treatment options that allow implementation of a personalized approach to cancer treatment. Large-scale genomic studies initially focused on the most common forms of bladder cancer. However, as genomic and molecular technologies become more widespread and are applied to less common variant histologies, we are gaining additional insight into the unique molecular and genomic characteristics driving the biology of variant histologies of bladder cancer. In this review, we summarize the current state of knowledge of molecular alterations underlying the distinct tumor biology of plasmacytoid urothelial carcinoma and how these alterations may impact treatment options.

HER2 Expression in Bladder Cancer: A Focused View on Its Diagnostic, Prognostic, and Predictive Role

Bladder cancer (BC) is a heterogeneous disease from a molecular, morphological, and clinical standpoint. HER2 is a known oncogene involved in bladder carcinogenesis. Assessing HER2 overexpression as a result of its molecular changes in a routine pathology practice using immunohistochemistry might be a useful adjunct in several scenarios, namely (1) to correctly identify flat urothelial lesions and inverted urothelial lesions in the diagnostic setting; (2) to provide prognostic hints in both non-muscle invasive (NMI) and muscle invasive (MI) tumors, thus supplementing risk stratification tools, especially when evaluating higher-risk tumors such as those with variant morphology; (3) to improve antibody panels as a surrogate marker of BC molecular subtyping. Furthermore, the potential of HER2 as a therapeutic target has been only partly explored so far, in light of the ongoing development of novel target therapies.

Are We Ready to Implement Molecular Subtyping of Bladder Cancer in Clinical Practice? Part 2: Subtypes and Divergent Differentiation

Following several attempts to achieve a molecular stratification of bladder cancer (BC) over the last decade, a "consensus" classification has been recently developed to provide a common base for the molecular classification of bladder cancer (BC), encompassing a six-cluster scheme with distinct prognostic and predictive characteristics. In order to implement molecular subtyping (MS) as a risk stratification tool in routine practice, immunohistochemistry (IHC) has been explored as a readily accessible, relatively inexpensive, standardized surrogate method, achieving promising results in different clinical settings. The second part of this review deals with the pathological and clinical features of the molecular clusters, both in conventional and divergent urothelial carcinoma, with a focus on the role of IHC-based subtyping.

Pleural fluid metastasis of plasmacytoid urothelial carcinoma in comparison to micropapillary and conventional high-grade urothelial carcinoma: Cytologic and immuonohistochemical findings

Plasmacytoid urothelial carcinoma (PUC) is a rare but clinically aggressive variant of high-grade urothelial carcinoma (HGUC). Cytological features include single plasmacytoid neoplastic cells with N:C ratio around 0.5, eccentric nuclei, nuclear hyperchromasia, irregular nuclear membrane, and vacuolated cytoplasm. Micropapillary urothelial carcinoma (MPUC) is another clinically aggressive variant of HGUC that shares some overlapping features of PUC. The diagnosis of these two aggressive variants in pleural effusions can be challenging due to features mimicking adenocarcinoma, unusual immunochemistry profile, and confusion with differential diagnoses, especially when pertinent clinical information is unavailable. We present report on one case each of pleural fluid metastasis of PUC and MPUC respectively, and compare the findings with that of a metastatic conventional HGUC originally thought to be metastatic adenocarcinoma. The diagnosis of PUC was confirmed with immunohistochemical studies showing expression for cytokeratin, GATA-3, uroplakin II, and CD138, diminished or loss of E-cadherin membranous expression, negative expression for p63, p53, Epicam-BerEP4, Epicam-MOC31, and p120. The diagnosis of MPUC was confirmed with immunostain profile similar to that of PUC except positive stain for E-cadherin, p120, and p53. The diagnosis of HGUC was confirmed with immunohistochemical studies showing expression for cytokeratin, GATA-3, uroplakin II, p63, Epicam-BerEP4 (focal weak), and Epicam-MOC31. Our cases of metastatic urothelial carcinoma showed features mimicking adenocarcinoma and others, especially the MPUC and HGUC were diagnosed without prior tissue diagnosis of urothelial carcinoma. This report emphasizes the cytohistological and immunohistochemical details of urothelial carcinoma involving effusion fluid and discusses potential pitfalls in diagnosis.

Pathological complete response of plasmacytoid variant bladder cancer to pembrolizumab following genomic analysis

Introduction

Plasmacytoid variant bladder cancer is a rare variant of urothelial carcinoma that accounts for 1% of bladder cancers. Plasmacytoid variant urothelial carcinoma is characterized by an aggressive phenotype and poor clinical outcomes.

Case presentation

A 61‐year‐old woman presented with gross hematuria. Cystoscopy showed a 16‐mm solid tumor. Transurethral resection of the bladder tumor was performed, and the pathological diagnosis was invasive plasmacytoid variant urothelial carcinoma. Although the pathological T stage was pT1, computed tomography showed right obturator lymph node swelling. Since previous reports indicate poor response to chemotherapy for this disease, clinical sequencing was performed. Based on the high tumor mutation burden revealed, pembrolizumab was administered for 4 cycles, and computed tomography showed a partial response. Robot‐assisted radical cystectomy was performed, and a pathological complete response including the pelvic lymph node was observed.

Conclusion

Pembrolizumab may be a treatment option for plasmacytoid variant urothelial carcinoma following genomic analysis.