Coordinated Expression of ADC Targets ERBB2, TACSTD2, and NECTIN4 in Bladder Cancer: A Multi-Scale Transcriptomic and...

Antibody-drug conjugates (ADCs) targeting HER2 (encoded by ERBB2), Trop2 (TACSTD2), and Nectin-4 (NECTIN4) have demonstrated clinical activity in bladder cancer. However, the co-expression relationships among these three targets at both the transcriptomic and protein levels, and their spatial organization within the tumor microenvironment, remain incompletely characterized. To address this, we performed a multi-platform, multi-resolution analysis integrating ten bulk RNA-seq datasets (n = 1628 samples), six spatial transcriptomics datasets (10x Visium and Visium HD, n = 31 specimens), and multiplex immunofluorescence (mIF) staining on three paired tumor-adjacent normal bladder specimens. Pairwise Pearson correlation analyses were conducted for ERBB2, TACSTD2, and NECTIN4 across bulk transcriptomes and spatial compartments (tumor core, interface, and stroma). High-resolution co-expression hotspot mapping was performed using Visium HD data. Preliminary protein-level evidence was obtained using mIF, with quantitative three-dimensional surface plot reconstructions illustrating the spatial distribution of marker co-expression. Given the limited number of specimens (three paired tumor-normal samples), these findings should be regarded as exploratory and illustrative rather than definitive validation. Moderate-to-strong positive correlations among the three genes were consistently observed across all ten bulk datasets, with the strongest association between TACSTD2 and NECTIN4 (Pearson r up to 0.969). Spatial transcriptomic analyses recapitulated these positive correlations across all histopathological compartments, with the tumor core generally exhibiting the highest coefficients. No consistent spatial gradient was observed, indicating preservation of co-expression across tissue niches. Visium HD analysis confirmed positive pairwise correlations and identified discrete co-expression hotspots. mIF revealed extensive Trop2-Nectin-4 protein colocalization across all tumors, whereas HER2 showed more restricted and heterogeneous expression. Triple-positive subpopulations were identified but were limited. Strikingly, all three markers exhibited pronounced tumor-specific upregulation relative to paired adjacent normal tissues, with surface plot analysis showing markedly elevated cumulative fluorescence intensities in tumors (Z-values approaching 240 arbitrary units) compared with a flattened landscape in normal tissues (Z-values < 100-120 arbitrary units). These findings provide a multi-scale description of ADC-target co-expression in bladder cancer and generate hypotheses for biomarker-driven patient stratification, which require validation in larger, independent cohorts.