Frequent overexpression of NECTIN-4 in CNS metastases from urothelial carcinoma.

804 Background: The combination of enfortumab vedotin plus pembrolizumab (EV/P) has become the new standard of care for advanced or metastatic urothelial carcinoma (mUC) due to its high efficacy. However, patients with active central nervous system (CNS) metastases were excluded from the EV-302 trial. More recently, NECTIN-4 amplifications have been identified as genomic predictors of EV response and long-term survival in patients with mUC. Additionally, early evidence suggests that EV may cross the blood-brain barrier and be effective in patients with CNS metastases. Therefore, we aimed to evaluate NECTIN-4 expression and amplification in patients with mUC involving CNS metastases. Methods: Immunohistochemical staining for NECTIN-4, with H-score evaluation, was performed in both non-CNS mUC (n=152) and CNS mUC patient cohorts (n=17). In addition, we developed a NECTIN-4-specific fluorescence in situ hybridization (FISH) assay to correlate NECTIN-4 copy number variations (CNVs) with membranous NECTIN-4 protein expression in CNS mUC. Results: Membranous NECTIN-4 protein expression was more abundant in CNS mUC (n=12/17; with H-score ≥ 100; median H-score 160; interquartile range [IQR] 250-85) than in non-CNS mUC samples (n=58/152; median H-score 40; IQR 0-140, p<0.001). Amplification data are currently being generated and will be presented at the conference. Conclusions: The substantial expression of NECTIN-4 in CNS metastases from UC, along with the results of the EV-302 trial and the identification of NECTIN-4 amplifications as genomic predictors of EV response and long-term survival in patients with mUC, supports the potential use of EV/P in treating patients with CNS mUC.