Abstract Background Although traditionally regarded as a vestigial organ, the appendix is increasingly recognized for its potential role in modulating gut immunity 1,2. The ACCURE trial suggested that appendicectomy is superior to standard medical therapy alone in maintaining remission in patients with ulcerative colitis (UC) 3. The underlying mechanisms linking the appendix to these immune and pathological processes remain poorly understood. In our previous studies, we observed that, in UC patients, immune surveillance governs the fate of the carcinogenesis progression 4. The current study aims to characterize the immune microenvironment of the normal mucosa surrounding UC-related rectal cancer and to define the effect of appendicectomy on it. Methods We analysed the healthy mucosa of patients with UC-related rectal cancer and patients with sporadic rectal cancer recruited in the prospective cohort of our project IMMUNOREACT (NCT04915326 and NCT04917263). Tissue samples were obtained from the cancerization field, the normal mucosa surrounding the rectal cancer. Transcriptomic analysis was performed with the PanCancer Immuno-Oncology 360TM panel (NanoString Technology). A panel of immune markers was investigated at flow cytometry (epithelial cells expressing CD80, CD86, HLA-ABC, and activated CD8+ T cells, CD4+ Th1 cells, and T reg). Results Transcriptomic analysis was performed in 4 UC-related rectal cancer patients and in 8 sex, age and stage matched sporadic rectal cancer patients and it showed that the mucosa of UC-related rectal cancer patients presents increased lymphocytic infiltration and activation, with particular increases in B-cell and neutrophil signatures, accompanied by alterations in epithelial markers and some innate/IFN pathways compared to sporadic rectal cancer (Fig. 1A). Flow cytometry was performed on UC-related rectal cancer (4 patients who had a previous appendicectomy compared to 7 who had not). In patients who had a previous appendicectomy, total lymph nodes retrieved at rectal resection were significantly less (p = 0.05)(Fig.1B). In these patients, epithelial cells in the cancerization field expressed significantly less costimulatory molecule CD86 than in patients who had not appendicectomy (p = 0.05)(Fig. 1C). Conclusion Although our study is limited by a small sample size, it showed that the normal mucosa immune microenvironment has a distinct profile in UC-related rectal cancer compared to sporadic rectal cancer. Moreover, in patients with UC-related rectal cancer and previous appendicectomy, epithelial cells in the cancerization field expressed significantly less costimulatory molecule CD86 suggesting an impaired antigen presentation in these patients that may have favoured or accelerated carcinogenesis. References: 1. Collard MK, Tourneur-Marsille J, Uzzan M, Albuquerque M, Roy M, Dumay A, Freund JN, Hugot JP, Guedj N, Treton X, Panis Y, Ogier-Denis E. The Appendix Orchestrates T-Cell Mediated Immunosurveillance in Colitis-Associated Cancer. Cell Mol Gastroenterol Hepatol. 2023;15(3):665-687. 2. Scarpa M, Castagliuolo I, Patuzzi I, Kotsafti A, Stepanyan A, Armellin C, Tagliente G, Savarino E, Zingone F, Ruffolo C, Saadeh L, Spolverato G, Angriman I, Scarpa M. Distinct microbiota composition and dendritic cell activation in the appendix microenvironment of ulcerative colitis patients. Gut Microbes. 2025 Dec;17(1):2545416. doi: 10.1080/19490976.2025.2545416. 3. ACCURE Study Group. Appendicectomy plus standard medical therapy versus standard medical therapy alone for maintenance of remission in ulcerative colitis (ACCURE): a pragmatic, open-label, international, randomised trial. Lancet Gastroenterol Hepatol. 2025 Jun;10(6):550-561. doi: 10.1016/S2468-1253(25)00026-3. 4. Kotsafti A, DʼIncà R, Scarpa M, Fassan M, Angriman I, Mescoli C, Bortoli N, Brun P, Bardini R, Rugge M, Savarino E, Zingone F, Castoro C, Castagliuolo I, Scarpa M. Weak Cytotoxic T Cells Activation Predicts Low-Grade Dysplasia Persistence in Ulcerative Colitis. Clin Transl Gastroenterol. 2019 Jul;10(7):e00061. doi: 10.14309/ctg.0000000000000061. Conflict of interest: Matteazzi, Anna: Scarpa, Melania: No conflict of interest Kotsafti, Andromachi: No conflict of interest Galuppini, Francesca: No conflict of interest Stepanyan, Astghik: No conflict of interest Tussardi, Gaia: No conflict of interest Scognamiglio, Federico: No conflict of interest Rosato, Antonio: No conflict of interest Ruffolo, Cesare: No conflict of interest Salmaso, Roberta: No conflict of interest Saadeh, Luca: No conflict of interest Rollo, Elena: No conflict of interest Spolverato, Gaya: No conflict of interest Luisetto, Roberto: No conflict of interest Di Camillo, Barbara: No conflict of interest Castagliuolo, Ignazio: No conflict of interest Fassan, Matteo: No conflict of interest Dei Tos, Angelo Paolo: No conflict of interest Angriman, Imerio: No Dr. Scarpa, Marco: No conflict of interest
Matteazzi et al. (Thu,) studied this question.