Clinical Significance of Histologic Variants of Bladder Cancer.

Pathologists have identified many "histologic variants" of bladder cancer (BCA): histologic patterns that differ from conventional urothelial carcinoma (transitional cell carcinoma). Several of these are biologically aggressive, and their identification may aid in clinical decision-making. This article reviews several histologic variants and their value in deciding management of cT1 disease and predicting response to neoadjuvant chemotherapy (NAC). Diagnostic issues are also addressed, such as interobserver variability among pathologists. For example, although stage cT1 conventional urothelial carcinoma is usually managed conservatively, cT1 micropapillary carcinoma has high mortality following conservative management, and early cystectomy may reduce mortality. Similarly, plasmacytoid and small cell cancers are remarkably aggressive, and those diagnosed as stage cT1 at transurethral resection are likely understaged; conservative management thus greatly risks undertreatment. As an example of response, NAC dramatically reduces mortality in patients with small cell BCA, and is thus the standard of care, even in stage cT1 disease. Although identification of histologic variants may inform on optimal management, diagnostic issues challenge their incorporation into clinical practice. For example, interobserver reproducibility is only moderate for the diagnosis of micropapillary BCA. Studies have identified specific histologic issues underlying this diagnostic irreproducibility, and ongoing work aims to remedy this issue. In summary, histologic variants are emerging as potentially useful biomarkers in the management of BCA. Although issues remain unresolved, pathologists and treating physicians will benefit from understanding these variants and their prognostic and therapeutic implications.