576P Prognostic values of a modified diagnostic biopsy-adapted immunoscore based on double immunohistochemical staining in patients with locally advanced rectal cancer

Tumor immune contexture plays a crucial role in the outcome of cancer patients. The aim of this study was to evaluate the prognostic value of the modified diagnostic biopsy-adapted immunoscore (mISb) for patients with locally advanced rectal cancer (LARC). We included 181 LARC patients from a single sub-center of a prospective study (NCT02533271), with 151 (83.4%) receiving surgical treatment and 30 (16.6%) following a watch-and-wait (W&W) strategy. Tumor biopsy tissues were stained using dual immunohistochemistry for CD8+ and CD3+ T cell densities, and the CD8/CD3 ratio was calculated. mISb was developed using mean percentile values of CD8+ T cell density and CD8/CD3 ratio, and patients were classified into low (0%-25%), intermediate (>25%-70%), and high (>70%-100%) mISb groups. Spearman correlation analysis was performed. Kaplan-Meier survival analysis, multivariate Cox regression models were used to assess the prognostic value of mISb for disease-free survival (DFS), and the role of mISb in the W&W strategy was further investigated. A strong correlation was found between CD8+ and CD3+ T cell densities (R=0.86, P<0.001), and a weaker correlation with the CD8/CD3 ratio (R=0.45). In the low, intermediate, and high mISb groups, there were 35 (23.2%), 84 (55.6%), and 32 (21.2%) patients, respectively. The respective 3-year DFS rates for these groups were 59.0%, 69.5%, and 80.1% (P=0.01). Multivariate analysis in surgically treated patients revealed mISb as an independent prognostic factor for DFS (intermediate vs. high: HR=2.38, 95% CI: 0.92-6.16, P=0.08; low vs. high: HR=3.69, 95% CI: 1.35-10.07, P=0.01). Among W&W patients, 6 (37.5%) in the mISb≤50% group experienced local-region or distant metastases, while only 1 (7.1%) in the mISb>50% group had local-region recurrence. mISb, as a potentially valuable prognostic indicator, demonstrates significant importance in assessing the prognosis of LARC patients. Future research is needed to further investigate the clinical application of mISb in rectal cancer prognosis, particularly in the context of the W&W strategy.