Abstract LB012: EphA2 expression across molecular and histological subtypes in muscle-invasive bladder cancer (MIBC) and its association with Nectin-4 and HER2

Abstract Background: MIBC is associated with poor prognosis despite aggressive multimodal therapy. Nectin-4- and HER2-targeting agents have shown benefit in patients (pts) with bladder cancer, including MIBC. EphA2 is another therapeutic target that may have potential in MIBC. Data for pts with variant and divergent histologies are limited, including a lack of information on EphA2 expression across MIBC subtypes, or its correlation with other potential targets. In a comprehensive MIBC tissue microarray, EphA2 and Nectin-4 expression were correlated to MIBC histological and molecular subtypes to identify potential pts best served by EphA2-targeted therapy. Methods: Tumor samples were grouped by consensus molecular (based on transcriptome signature) and histologic subtype. Membrane protein expression of EphA2, Nectin-4, and HER2, plus RNA expression, were quantified by IHC and whole-transcriptome sequencing, respectively. For membranous EphA2 and Nectin-4 expression, the difference in H-score (H-diff) was assessed via the Kruskal-Wallis test. HER2 status was assessed using the gastric algorithm. RNA transcript levels were quantified using Kallisto V0.44. A tumor proportion score >1 was used to define EphA2 positivity. Results: Membranous EphA2 was expressed in 34% and 36% of MIBC pts (N=234 molecular and N=285 histological subtype analysis), with expression significantly higher in pts with Ba/Sq (40%, n=110) vs luminal unstable [LumU] (5%, n=22) and neuroendocrine [NE]-like (0%, n=9) molecular subtypes (p=0.012) and in pts with Sq (46%, n=76) vs NE (0%, n=10) histology (p=0.028). Conversely, Nectin-4 membranous expression was significantly lower among pts with molecular Ba/Sq vs stroma-rich/luminal papillary/LumU/luminal non-specified subtypes (H-diff p=1.1e-14) and Sq vs variant/not otherwise specified histology (H-diff p=1.4e-15). Ba/Sq molecular or Sq histological subtypes represented 47% and 27% of their respective datasets. Pts with Sq histology or Ba/Sq molecular subtypes had a higher prevalence (40% or 35%, respectively) of EphA2-positive and HER2-negative tumors than other subtypes. Among pts with Sq histology and Ba/Sq molecular subtype, 29% and 26% were EphA2-positive, Nectin-4 negative, and HER2-negative, respectively. In matched samples (N=241), there was no correlation between NECTIN4 (R2=0.02) or ERBB2 (HER2) (R2=0.028) with EPHA2 RNA expression. This was also the case in matched samples for pts with Ba/Sq molecular (R2=0.011) and Sq (R2=0.063) histological subtypes. Conclusions: These data indicate that MIBC pts with a Ba/Sq molecular subtype and/or Sq histology may benefit from EphA2-targeted treatment, warranting further investigation of EphA2 as a novel therapeutic target in MIBC and other bladder cancers. Citation Format: Markus Eckstein, Qin Tjokrosurjo, Stephen J. Blakemore, Daniel A. Peterson, Kevin Magalhaes, Johannes Brägelmann, Niklas Klümper. EphA2 expression across molecular and histological subtypes in muscle-invasive bladder cancer (MIBC) and its association with Nectin-4 and HER2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(8_Suppl):Abstract nr LB012.