FGFR3 expression in primary and metastatic urothelial carcinoma of the bladder

Abstract While fibroblast growth factor receptor 3 ( FGFR 3) is frequently mutated or overexpressed in nonmuscle‐invasive urothelial carcinoma ( UC ), the prevalence of FGFR 3 protein expression and mutation remains unknown in muscle‐invasive disease. FGFR 3 protein and mRNA expression, mutational status, and copy number variation were retrospectively analyzed in 231 patients with formalin‐fixed paraffin‐embedded primary UC s, 33 metastases, and 14 paired primary and metastatic tumors using the following methods: immunohistochemistry, NanoString nCounterTM, OncoMap or Affymetrix OncoScanTM array, and Gain and Loss of Analysis of DNA and Genomic Identification of Significant Targets in Cancer software. FGFR 3 immunohistochemistry staining was present in 29% of primary UC s and 49% of metastases and did not impact overall survival ( P = 0.89, primary tumors; P = 0.78, metastases). FGFR 3 mutations were observed in 2% of primary tumors and 9% of metastases. Mutant tumors expressed higher levels of FGFR 3 mRNA than wild‐type tumors ( P < 0.001). FGFR 3 copy number gain and loss were rare events in primary and metastatic tumors (0.8% each; 3.0% and 12.3%, respectively). FGFR 3 immunohistochemistry staining is present in one third of primary muscle‐invasive UC s and half of metastases, while FGFR 3 mutations and copy number changes are relatively uncommon.