Abstract
3544 Background: Signet-ring cell carcinoma (SRCC) of the rectum and sigmoid colon is a rare and highly malignant challenge in clinical practice. Although high PD-1+CD8+ tumor-infiltrating lymphocyte (TIL) infiltration has been reported as a positive prognostic factor in gastric cancer, pancreatic cancer, etc., its role in colorectal SRCC remains unclear. This study aims to explore the immune landscape of colorectal SRCC and its prognostic implications. Methods: The study included 34 patients with stage II-IV SRCC of the rectum and sigmoid colon. The immune contextures of tumor tissues were characterized using multiplex immunofluorescence assays and compared with a cohort of 57 cases of stage II-IV AC. The ratio density and spatial distribution of CD3+, CD8+, PD-1+, PD-L1+ cells, M1/M2 macrophages, and NK cells were quantitively analyzed in both parenchymal (p) and interstitial (i) regions. Characteristics of immune cell infiltration and their prognostic value for long-term survival were investigated in SRCC cases. Results: Compared to AC, SRCC exhibited significantly higher infiltration of CD8+ and CD3+ iTILs in the interstitial region (P=0.00024; P=0.00321, respectively) and elevated CD8+ pTILs infiltration in tumor parenchyma (P=0.041). Conversely, parenchymal infiltration of TILs co-expressing PD-1 was significantly lower in SRCC than AC (PD-1+CD8+ pTILs: P=0.00035; PD-1+CD3+ pTILs: P=5.0e-05). SRCC showed significantly lower infiltration of M1 macrophages in both parenchyma and interstitium (P=0.0035; P=5.4e-09, respectively), lower interstitial infiltration of M2 macrophages (P=1.5e-05), and a borderline lower parenchymal infiltration of M2 macrophages (P=0.0522), compared to AC. Additionally, patients with high parenchymal or interstitial infiltration of PD-1+CD8+ TILs exhibited significantly longer DFS (P=0.00024; P=0.0041, respectively) and OS (P=0.011; P=0.0044, respectively) than those with low infiltration. Multivariate analysis indicated that the level of PD-1+CD8+ pTILs infiltration is an independent prognostic factor for DFS, being independent of CEA levels and TNM stage (P = 0.018; P = 0.02, respectively). Among patients with normal CEA level or of stage II-III, high level of PD-1+CD8+ pTILs infiltration was still associated with significantly improved DFS (P<0.0001; P=0.00018, respectively) and OS (P=0.00021; P<0.0001, respectively). Conclusions: SRCC of rectum and sigmoid colon exhibits distinct immune profiles compared to conventional AC, characterized by higher infiltration of CD8+ and CD3+ TILs, but lower infiltration of PD-1+CD8+ TILs. The unique immune landscape in SRCC, particularly the level of PD-1+CD8+ TILs infiltration and its positive predictive value for DFS and OS, provides new perspectives for immune-based stratification and therapeutic strategies for this clinically significant cancer subtype.
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