A total of 473 patients (mean age: 63 years; 73% male) underwent resection, 51% 2-stage, 18% 3-stage, 12% transhiatal, and 19% extended total gastrectomy. Ninety-six (20%) patients developed new-onset AF, in 18%, 27%, 29%, and 14% of 2-, 3-, transhiatal, and extended total gastrectomy cohorts, respectively (P=0.05). Age, diabetes, neoadjuvant therapy, and cardiac history predisposed (P<0.05) to AF, and AF was significantly (P<0.0001) associated with pneumonia, pleural effusions requiring drainage, and maximum postoperative C-reactive protein (CRP) (P<0.05) but not with anastomotic leak/conduit necrosis or mortality. Amiodarone was the primary treatment in 63% of cases, 1% underwent cardioversion, and 92% were in sinus rhythm on discharge. At a median follow-up of 40 months (7-109 months), the median survival was 40 months versus 53 months in the AF and non-AF cohorts, respectively (P=0.353) CONCLUSIONS: New-onset AF is common, linked to age, diabetes, cardiac disease, and neoadjuvant therapy. It is strongly associated with complications, principally respiratory sepsis, and systemic inflammation. For most, it resolves, with no impact on oncologic outcomes.

Introduction Selection criteria for immunotherapy with checkpoint blockade in colorectal cancer are currently based on mismatch repair status. However, intra-tumoral T cell response varies among patients with the same MMR status. Inhibitory checkpoint expression on tumour-infiltrating lymphocytes in microsatellite stable and unstable CRC is unknown. Method Flow cytometric analysis and single-cell RNA sequencing, using the 10x genomic platform, were performed ex vivo on tumour and uninvolved colonic tissue samples from patients undergoing surgical resection for colorectal cancer. Inhibitory checkpoint expression (PD-1) and functional status of isolated populations of TILs were analysed. Result Conventional and unconventional tissue-resident T cells were enriched in tumour samples compared to uninvolved healthy colonic tissue. Upregulation of PD-1 expression on TILs was observed in all patients, however the % upregulation varied among those with the same MMR status. A proportion of MSS tumours were found to have high levels of PD-1 expression, while a subset of MSI tumours had low PD-1 expression. Functional studies of cytotoxicity demonstrated varying TIL production of IFNg, TNFa and amphiregulin in patients with the same MMR status. Conclusion TIL profile (infiltration pattern, checkpoint expression and functional status) differs among patients with the same MMR status. A subset of ‘hot’ immunogenic MSS tumours exist that may respond to checkpoint blockade. Characterisation of TIL profile represents a more accurate method of selecting patients likely to derive benefit. Abbrev. CRC Colorectal cancer, MMR Mismatch repair, TIL Tumour-infiltrating lymphocytes, MSS Microsatellite stable, MSI Microsatellite unstable, IFNg Interferon-gamma, TNFa Tumour necrosis factor alpha Take-home message A subset of immunogenic microsatellite stable colorectal tumours exist that may respond to checkpoint blockade. Mismatch repair status alone does not accurately predict response to immunotherapy.

Colorectal cancer is the third most common malignancy worldwide, with increasing numbers due to the spreading obesity epidemic and Western diet. Colorectal tumors are subclassed by mutational burden, caused by microsatellite instability (MSI). MSI-high tumors tend to induce robust T-cell responses and respond well to immunotherapy. However, microsatellite-stable (MSS) tumors lack high mutational burden and conventional T-cell recognition. While these tumors have therefore been considered immunologically “cold,”, MSS tumors are infiltrated by innate lymphocytes, including gd T cells, natural killer (NK) cells, and mucosal associated invariant T (MAIT) cells. We therefore focused on the innate antitumor response in these patients. Colon tumor and uninvolved tissue were sampled from 6 patients undergoing surgical resection for MSS tumors. Using the 10x genomics platform, single-cell RNAseq was performed on isolated populations of gd T cells, NK cells, MAIT cells, and conventional T cells. Single-cell analysis of these tumors revealed significant heterogeneity in all cell subsets analyzed, revealing phenotypic and functional changes not previously observed in bulk sequencing data. A subset of gdT cells adopted a wound healing phenotype in all colorectal cancer samples. These soluble factors are involved in the tissue repair response and barrier integrity, providing mitogenic signals to epithelial cells. In addition, they are associated with immune suppression and induction of regulatory T cells. In humans, this phenotype can be induced in Vd1 T cells in response to proinflammatory cytokine stimulation. In the murine gut, resident gd T cells adopt this phenotype basally and increase production in response to inflammatory cytokine production. The combination of pro-tissue growth and immune suppression, by gd T cells, likely contributes to the poor immunogenicity of MSS tumors. Depleting or converting these cells represents a novel immunotherapeutic target in colorectal cancer. Citation Format: Cathal Harmon, Alex Zaborowski, Harry Kane, Stephen Cunningham, Leandro Agudelo, Manolis Kellis, Des Winter, Lydia Lynch. scRNA-seq reveals functionally distinct gd T cells in human colorectal tumors [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A47.