Changes in the inflammatory microenvironment in premalignant colonic adenomatous polyps: Evidence for immunosurveillance?
535 Background: The majority of colorectal cancers develop through the adenoma-carcinoma sequence. Recently, the host inflammatory response has become recognized as a key determinant of outcome. In particular, a pronounced peri-tumoral local inflammatory infiltrate identifies those with a better outcome. The present study aimed to characterize the local inflammatory response in pre-malignant colorectal adenomatous polyps. Methods: Patients with adenomatous polyps removed at colonoscopy as part of a population FOBt screening program were identified from a prospectively maintained database. All polyps were greater than 1cm. Whole slide immunohistochemistry was performed to assess intraepithelial T-cell (CD3+), cytotoxic T-cell (CD8+) and macrophage (CD68+) infiltrate. Inter-observer agreement for assessment of inflammatory cell infiltrate was good or better for CD3+, CD8+ and CD68+staining (Kappa 0.66, 0.66, 0.79 respectively). Results: A total of 207 adenomatous polyps, 107 high-grade (HG), 100 low-grade (LG), from 134 patients were included. Median age was 65 years, 33 (25%) were female and 15 (11%) were taking regular aspirin. Comparing HG and LG polyps, there were more older and female patients in the HG group (p<0.05). There was no difference in location (p=0.222), macroscopic morphology (p=0.445) or aspirin (p=0.377) use between groups. Microscopically, HG polyps were more likely to contain a villous component than LG polyps (65% vs 50%, p<0.05). Overall, high levels of CD3+, CD8+ and CD68+ infiltrate were observed in 68%, 25% and 72% of polyps respectively. Both CD3+ (74% vs 61%, p<0.05) and CD8+ (37% vs 13%, p<0.001) infiltrate was higher in HG polyps compared to LG polyps. There was no association with polyp grade and CD68+infiltrate (74% vs 70%, p=0.540). Conclusions: An increase in local T-lymphocytic infiltrate, but not macrophage infiltrate was identified with progression from low-grade to high-grade dysplasia. This would suggest a specific response to early disease progression confirming increased immunosurveillance. Therefore, such early stage disease may amenable to immunomodulatory treatment.