Occurrence of NECTIN4 amplification in solid tumors and enfortumab vedotin response in metastatic urothelial cancer.

673 Background: The anti-NECTIN4 antibody-drug conjugate (ADC) enfortumab vedotin (EV) is approved for patients with metastatic urothelial cancer (mUC). However, durable benefit is only achieved in a small, yet uncharacterized patient subset. NECTIN4 is located on chromosome 1q23.3, and 1q23.3 gains are frequent genomic events in mUC leading to NECTIN4 amplifications. Here, we aimed to evaluate the potential of NECTIN4 amplification as a genomic biomarker to predict EV response in patients with mUC. Methods: We established a NECTIN4-specific fluorescence in-situ hybridization (FISH) assay to assess NECTIN4 copy number variations (CNVs) in a multicenter EV-treated mUC patient cohort (UC-EV, N=77), and CNV data were correlated with membranous NECTIN4 protein expression (H-score) assessed via immunohistochemistry, EV treatment responses and outcomes. Next, we conducted a pan-cancer analysis of the The Cancer Genome Atlas (TCGA) datasets, comprising 10,712 patients across 32 cancer types, to investigate the relationship between NECTIN4 CNV, mRNA expression (RNAseq) and protein levels (RPPA) across entities. Results: In TCGA cohorts, NECTIN4 amplification occurs frequently across different solid cancer types, especially in 15-20% of bladder cancers (17% in TCGA-BLCA), as well as 5-10% in breast cancer (TCGA-BRCA) and lung adenocarcinoma (TCGA-LUAD). We confirmed the amplification frequency in our UC-EV cohort (18%). NECTIN4 amplification is significantly associated with both increased NECTIN4 mRNA expression (e.g., TCGA-BLCA, BRCA, LUAD) and membranous NECTIN4 protein expression (UC-EV), and represents a stable genomic alteration during metastatic progression. In the UC-EV cohort, all patients with NECTIN4 amplification (N=14) responded to EV. In multivariable Cox adjusted for age and sex, NECTIN4 amplifications led to a 93% risk reduction for death compared to a NECTIN4non-amplified status (HR=0.07, 95%-CI 0.01–0.53; P<0.001). Conclusions: Our study highlights the value of NECTIN4 amplifications to predict EV responses in patients with mUC. NECTIN4 amplifications occur frequently in different cancer types and therefore have the potential to be a novel tumor-agnostic genomic biomarker that enables tailored NECTIN4-targeted therapies in various entities.