Profiling Fibroblast Growth Factor Receptor 3 Expression Based on the Immune Microenvironment in Upper Tract Urothelial Carcinoma

Background Although several studies have shown favorable outcomes in upper tract urothelial carcinoma (UTUC) with fibroblast growth factor receptor 3 (FGFR3) mutations and/or expression, the relationship between immune cell markers and FGFR3 expression remains unknown. Objective To clarify the FGFR3-based immune microenvironment and investigate biomarkers to predict the treatment response to pembrolizumab (Pem) in patients with UTUC. Design, setting, and participants We conducted immunohistochemical staining in 214 patients with UTUC. The expression levels of FGFR3, CD4, CD8, CD68, CD163, CD204, and programmed cell death ligand 1 (PD-L1) were examined. Intervention All UTUC patients underwent radical nephroureterectomy. Outcome measurements and statistical analysis We assessed the relationship between these immune markers and patient prognosis. Results and limitations A total of 109 (50.9%) patients showed high FGFR3 expressions and a favorable prognosis compared with the remaining patients. Among the six immune markers, CD8 high expression was an independent favorable factor, whereas CD204 expression was an independent prognostic factor for cancer death. From the FGFR3-based immune clustering, three immune clusters were identified. Cluster A showed low FGFR3 with tumor-associated macrophage–rich components (CD204+) followed by a poor prognosis due to a poor response to Pem. Cluster B showed low FGFR3 with an immune hot component (CD8+), followed by the most favorable prognosis owing to a good response to Pem. Cluster C showed high FGFR3 expression but an immune cold component, followed by a favorable prognosis due to the high FGFR3 expression, but a poor response was confirmed with Pem. Conclusions Although most patients exhibit a poor response to Pem, individuals with low FGFR3 expression and immune hot status may benefit clinically from Pem treatment. Patient summary We conducted immunohistochemical staining to evaluate fibroblast growth factor receptor 3 (FGFR3)-related immune microenvironment by evaluating the expressions of CD4, CD8, CD68, CD163, CD204, and PD-L1 in 214 upper tract urothelial carcinoma patients. We identified three distinct immune clusters based on FGFR3 expressions and found that patients with a low FGFR3 expression but immune hot status received the maximum benefit from an immune checkpoint inhibitor.