Best practices recommendations in the application of immunohistochemistry in the bladder lesions: report from the International Society of Urologic Pathology consensus conference.

The bladder working group of the 2013 International Society of Urologic Pathology (ISUP) Conference on Best Practices Recommendation in the Application of Immunohistochemistry (IHC) in Urologic Pathology discussed 5 settings in which IHC is commonly used in clinical practice. With regard to markers for urothelial differentiation, the committee found that there is no ideal marker or established panel to confirm urothelial differentiation. On the basis of the differential diagnostic consideration, positivity for GATA3, CK20, p63, and either high-molecular weight cytokeratin (HMWCK) or cytokeratin (CK)5/6 is of value in proving urothelial differentiation in the appropriate morphologic and clinical context. With regard to the role of IHC in the distinction of reactive atypia from urothelial carcinoma in situ, the committee recommended that morphology remains the gold standard in this differential diagnosis and that, at best, the IHC panel of CK20/p53/CD44(s) has potential utility but is variably used and has limitations. The immunostaining pattern must be interpreted with strict morphologic correlation, because overreliance on IHC may be misleading, particularly in the posttreatment setting. IHC has no role in the distinction of dysplasia versus carcinoma in situ and in the grading of papillary urothelial carcinoma. IHC may have a limited but distinct role in staging of bladder cancer. In a subset of cases, depending on the clinical and histologic context, broad-spectrum cytokeratins (to identify early or obscured invasion) and desmin (distinction of muscle from desmoplasia and to highlight muscle contours for subclassification) may be helpful. Limited experience and conflicting data preclude smoothelin or vimentin to be recommended routinely for subclassifying muscle type at this time. In the workup of a spindled cell proliferation of the bladder and in limited specimens, we recommend an immunohistochemical panel of 6 markers including ALK1, SMA, desmin, cytokeratin (AE1/AE3), and p63 with either of HMWCK or CK5/6. Currently, there are no prognostic immunohistochemical or molecular studies that are recommended to be routinely performed on biopsy or resection specimens.