We introduce a model to describe tumor development. The model takes into account the development of their own cells, the effects of chemotherapeutic drugs on them, as well as their interaction with surrounding cells. We also introduce an analytical approach for the analysis of the introduced model. The approach gives the possibility to take into account changes in the conditions of the processes considered: changes in the properties of tissues in space and time, as well as the nonlinearity of the development of tumors. We analyzed the possibility of accelerating and decelerating the development of the tumor depending on the parameters of the considered process. The possibility of changing their rates is being considered.