In this proceedings we present part of our work in progress about modelling and analysis of tumor growth evolution. Here we focus on tumor-immune system interactions during the most aggressive stage of the cancer disease, when tumor cells are able to use the mechanisms developed in a previous stage to avoid the immune system. In particular, we incorporate in our modelling both the effects of adoptive cellular immunotherapy by activated immune cells and the time lag used by the activated immune cells to give a response after recognizing the tumor cells. We propose a delayed model of ordinary differential equations describing these effects and investigate the well-posedness of the system, equilibrium states and stability properties and the impact of the time delay on the dynamics. Some numerical simulations are shown to illustrate the outcomes of the model and the results are commented in light of the cancer developing.