Intratumoral immune landscape changes after neoadjuvant chemoradiation in esophageal cancer.

443 Background: Neoadjuvant chemoradiation (nCRT) remains a standard of care in esophageal cancer. Although adjuvant Nivolumab improves progression-free survival (PFS), 5-year overall survival (OS) remains suboptimal. It is uncertain if PDL1 expression is a useful predictive biomarker in this setting. This study prospectively evaluated intratumoral immune changes after nCRT and their associations with clinical outcomes. Methods: All patients were treated with the CROSS regimen (41.4Gy in 23 fractions with weekly paclitaxel & carboplatin) followed by surgery. Multiplex immunofluorescence was performed on paired pre-CRT and post-CRT FFPE sections, staining for CK, CD3, CD8, CD68, FOXP3 and PDL1. Images were captured using Zeiss Axioscan 7 slide scanner and analyzed by a pathologist using HALO v3.6 software. The average percentage staining was calculated. Pathological tumor response was centrally reviewed. Data were presented as median (IQR). Changes in the immune cell densities before and after nCRT were compared using Wilcoxon signed-rank test. Locoregional recurrence-free survival (LRRFS), PFS and OS were defined from time of diagnosis. Univariate Cox regression analysis was used to assess the effects of immune cell densities on survival outcomes. A p <0.05 was considered statistically significant. Results: Twenty patients (85% males, 75% SCC) were included. R0 resection and pathological complete response (pCR) were achieved in 55% (11/20) and 15% (3/20) of patients, respectively. Significant reduction in PDL1+ tumor cells (∆ -0.2%, IQR -2.1 – 0.0, p = 0.044), FOXP3+ regulatory T-cells (T reg ) (∆ -0.4%, IQR -0.6 – -0.2, p <0.001) and PDL1+ macrophages (∆ -0.4%, IQR -0.9 – 0.0, p = 0.014) were observed after CRT. No significant changes were observed in CD8+ T-cells and PDL1- tumor and immune cell densities. Pre-CRT and post-CRT changes in immune cell densities did not differ between pCR and non-pCR patients. Median follow-up was 6.0 years (3.4 – 6.4) for all patients. On univariate Cox regression, only circumferential resection margin (CRM) was associated with PFS (HR 0.20, 95% CI 0.06 - 0.69, p = 0.011) and OS (HR 0.11, 95% CI 0.02 - 0.54, p = 0.007). Pre-CRT and changes in immune cell densities after nCRT, pCR status, histology and gender were not associated with DFS, LRRFS and OS. Interestingly, one patient received adjuvant Nivolumab when this became standard-of-care but relapsed within 1 year of surgery. This patient had a reduction in PDL1+ tumour cells (0.2%) and PDL1+ macrophages (0.2%) after nCRT. Conclusions: Neoadjuvant CRT led to significant reduction in immunosuppressive cells including PDL1+ tumour and immune cells, and T reg . However, these changes were not associated with pCR or survival in this small study. Larger confirmatory studies are needed to guide future biomarker-driven adjuvant strategies in esophageal cancer.