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e14178 Background: Colorectal Cancer (CRC) is the third most commonly diagnosed cancer in the world. Yet, CRC has been difficult to treat with immunotherapy, as majority (85%) of CRC are Microsatellite stable (MSS), lowly immunogenic and do not respond well. To investigate immuno-cytotoxicity in MSS cancers, we set up an ex vivo co-culture model using patient-derived tumor epithelial cells and autologous tumor-infiltrating lymphocytes (TILs). Aims: To perform phenotypic and functional characterisation of the model, and show we are able to modulate immuno-cytotoxicity. Methods: Fresh tumor, adjacent normal and/or liver metastasis samples were collected and freshly dissociated from 29 colorectal cancer patients undergoing surgery. TILs and tumor epithelial cells were grown in culture. Weekly immunophenotyping of TILs was performed via flow cytometry and data was analysed to identify temporal changes in proportions of cell types. To modulate cytotoxicity, epithelial cell lines were co-cultured with autologous and allogeneic TILs at various effector:target ratios with and without anti-PD1 (Pembrolizumab). Caspase dye was used to detect apoptosis and measure cell death. Results: TILs from most patients were successfully expanded, with a theoretical potential of up to 10,000 times. CD4+ T cells were selectively expanded, while CD8+ T cells decreased in proportion over time. A select group of patients showed an opposite trend. Cell type proportions in metastases mirrored those of the primary tumour while NK cells expanded more in tumour samples than normal samples. Selection proceeded up to 3 weeks then decreased. In the cytotoxicity experiment, we show that cell death is increased at higher effector:target ratios in the presence of autologous TILs. Addition of Pembrolizumab further modulates cytotoxicity in vitro. Conclusions: We have developed and characterised an autologous T cell and epithelial cell co-culture system to evaluate immuno-cytotoxicity in colorectal cancer. This will allow screening of perturbations for improved immuno-cytotoxicity in colorectal cancer.

e15531Background: Response to immune checkpoint inhibition is dismal in colorectal cancer (CRC). There are limited experimental models to evaluate immunotherapy in human CRC. We developed an ex viv...

3589 Background: Insulin resistance and deregulation of the insulin-like growth factor (IGF) axis is implicated in colonic carcinogenesis. Metformin inhibits hepatic gluconeogenesis and increases insulin sensitivity. It induces AMPK activation, thus inhibiting mTOR and downstream survival and proliferation pathways. We evaluated the effects of metformin on survival outcomes of patients with stage 2 and 3 colorectal cancer (CRC). Methods: Among 1455 patients with stage II or III colorectal cancer, we identified 344 patients with both CRC and diabetes mellitus. 219 diabetic patients received metformin and 125 diabetic patients were not receiving metformin. Patient’s demographics, clinical and histopathologic characteristics, overall survival, time to recurrence and relapse-free survival were evaluated. Molecular analysis for AMPK, and mTOR pathway on archival tissue is ongoing. Results: After a median follow-up of 78 months (6.5 years), there was no difference in survival outcomes between diabetic and non-diabetic patients. Among diabetic patients, there were 99 relapses and 90 deaths. Metformin use was associated with improved overall survival (HR 0.23; 95%CI: 0.15-0.35 p