In this study, the investigators will establish a reliable method and logistic pipeline for personalized drug testing ex vivo using fresh tumor samples from colorectal cancer (CRC) patients. With this, the investigators aim to develop a novel predictive biomarker of immunotherapy response, by testing combinations of chemotherapies and chimeric antigen receptor (CAR) T cells. Critically, this affects a large subgroup of patients currently not considered to benefit from such treatment. To support the hypothesis, the project will make use of cutting-edge, cell-based functional diagnostics. Individual patients' cancer cells will be screened against a panel of chemotherapies and targeted therapies including CAR T cells, to assess the optimal combination of therapies to induce immunotherapy efficacy in otherwise unresponsive CRC.