Integrated morphologic, immunophenotypic, and molecular profiling of advanced upper tract urothelial carcinoma across tumor compartments supports biopsy-based testing.

FGFR3 alterations are well established in low-grade urothelial carcinoma, but their prevalence, stability, and biological significance in locally advanced and metastatic upper tract urothelial carcinoma remain only partially defined.

Immunohistochemistry included CK20, CK5, GATA3, p53, and mismatch repair proteins.

FGFR3 alterations were identified in 50% of patients and in 54.2% of analyzed tumors.

TP53 mutations co-occurred with FGFR3 alterations in 60% of FGFR3-mutated patients and showed 90.4% concordance with p53 immunohistochemistry.