Clinical efficacy and biomarker analysis of pre-operative ipilimumab plus nivolumab in stage III urothelial cancer: The NABUCCO trial update.

4593 Background: In the NABUCCO trial, pre-operative ipilimumab (ipi) + nivolumab (nivo) was studied in patients (pts) with stage III (cT3-4aN0M0 or cT1-4aN1-3M0) urothelial cancer (UC). In cohort 1 (C1), 11/24 pts (46%) achieved complete pathological response (ypT0N0). In cohort 2 (C2), two ipi/nivo dosing regimens were studied in 30 additional pts. The results suggest that a higher ipi dosage (3 mg/kg) is more effective in stage III UC. Here, we present an update on clinical efficacy and an exploratory biomarker analysis. Methods: In NABUCCO, UC pts received sequential ipi 3 + nivo 1 (ipi-high, C1; n=24) and combined ipi 3 + nivo 1 (ipi-high, C2A; n=15) or ipi 1 + nivo 3 (ipi-low, C2B; n=15), followed by radical cystectomy. The cut-off date for the updated survival analysis was March 31 th , 2023. Whole exome sequencing was performed on pre-treatment formalin-fixed paraffin-embedded (FFPE) tumor tissue and peripheral blood to call somatic variants. RNA from pre- and post-treatment FFPE tissue was isolated and sequenced. PD-L1 immunohistochemistry (clone 22C3) was performed on baseline FFPE tumor tissue and manually scored using the combined positivity score (CPS), tumor positivity score (TPS), and immune score (IC). To profile the tumor microenvironment, pre- and post-treatment FFPE slides were stained with three multiplex immunofluorescence (mIF) panels consisting of antibodies against CD3, CD20, FoxP3, PanCK, CD68, CD206, IRF8, CD8, CD103, and TCF1. Tumor areas were annotated manually and distinguished from stromal areas using a classifier and tissue segmentation. Results: After a median follow-up of 48 months, 2-year overall survival (OS) was 90% upon ipi-high (C1+2A) and 73% upon ipi-low (C2B). Progression-free survival (PFS) at 2 years was 75% upon ipi-high (C1+2A) and 67% upon ipi-low (C2B). Tumor mutational burden (TMB) was higher in responding pts (≤ypT1N0) across treatment arms (p=0.00068). Treatment response was associated with PD-L1 positivity (CPS p=0.048; TPS p=0.004; IC p=0.016). Increased RNA expression of immune-related genes such as IDO1, CTLA4, and PD-L1, and signatures of T-helper 1- and T-follicular helper cells at baseline were associated with response in pts treated in the ipi-low arm, but not in the ipi-high arms. Increased baseline RNA expression of a TGFβ signature was associated with non-response. Nonresponders to ipi/nivo demonstrated enhanced RNA expression of CD8 T-cell and stromal signatures. Pending results of the mIF analysis will be presented at ASCO 2024. Conclusions: Both OS and PFS at 2 years were numerically better in UC pts treated with a high ipi dose. Overall, TMB and PD-L1 positivity were associated with treatment response regardless of ipi dose. Pre-existing intratumoral T-cell immunity appeared to be required to induce an anti-tumor response in UC pts treated with ipi-low. Clinical trial information: NCT03387761 .