Prediction of response to neoadjuvant chemotherapy of patients with muscle invasive bladder cancer by molecular subtyping and radioligand target quantitation: Preview of the Bladder BRIDGister.

543 Background: Patients with muscle invasive urothelial carcinoma achieving pathological complete response (pCR) upon neoadjuvant chemotherapy (NACT) have improved prognosis. Molecular subtypes of bladder cancer differ markedly with regard to sensitivity to cisplatinum based chemotherapy and harbour FGFR treatment targets to various content. Previously we did show that lumina tumors respond better to NACT, while FGFR1 expression is associated with chemo resistance (Ecke et al. 2022). The objective of this study was to determine wether radioligand therapy may be an appropriate option in chemoresistent tumors to justify subsequent prospective validation within the "Bladder BRIDGister". Methods: Formalin fixed paraffin embedded (FFPE) tissues from transurethral resections (TUR) before chemotherapy and cystectomy samples after NACT of 36 patients were retrospectively collected. RNA from FFPE tissues were extracted by commercial kits, relative gene expression of subtyping markers (KRT5, KRT20, FGFR1) and radioligand target genes (CXCR4, FAP) were analyzed by standardized RT-qPCR systems (STRATIFYER Molecular Pathology GmbH, Cologne). Spearman correlation, hierarchical clustering, Kruskal-Wallis, chi square and contingency tests were done by JMP 9.0.0 (SAS software). Results: The neoadjuvant cohort consisted of 36 patients (median age: 69, male 83% vs. female 17%) with 92% of patients being histopathologically node negative. When comparing pretreatment with post treatment samples the median expression of KRT20 dropped 128fold, while FGFR1, CXCR4 and FAP mRNA expression increased 6,8fold, 1,9 fold and 2,9 fold, respectively. FAP was positively associated with KRT5, FGFR1 and CXCR4 in treatment naïve TUR biopsies (r=0.4051 p=0.0141, r=0.6458 p<0.0001 and r=0.7586 p<0.0001, respectively), but negatively associated with KRT20 (r=-0.3879 p=0.0194). As previously described, FGFR1 was negatively associated with pCR (r=-0.6418 p<0.0001). Similarly, CXCR4 and FAP trended to be negatively associated with pCR (r=-0.3181 p=0.0586; r=-0.3072 p=0.0684). Hierarchical clustering revealed that CXCR4 and FAP are elevated in stromal rich, KRT5 & KRT20 negative tumors not responding to NACT. Elevated FAP above median mRNA expression was significantly associated with resistance to NACT (chi2 4.314 p=0,0378). Combining elevated FAP and CXCR4 mRNA expression did identify 28% of the patients to be at high risk of NACT resistance (90%). Conclusions: Expression of the radioligand targets CXCR4 and FAP are associated with basal/stromal enriched tumors and resistance to NACT. Theranostic targeting of CXCR4 and FAP before NACT might increase response towards NACT in this poor prognosis group.