A mixed immunotherapy-chemotherapy treatment protocol is developed for cancer treatment. Immunotherapy alters the dynamics of the system by affecting on the parameters of the system, and then chemotherapy pushes the trajectory of the system toward the tumor-free equilibrium point. The chemotherapy protocol is derived using the pseudo-spectral controller. In this method, an infinite-horizon optimal control problem is proposed for a nonlinear cancer model. Then, the infinite-horizon optimal control of cancer is transformed into a nonlinear programming (NLP) problem. The efficient Legendre pseudo-spectral (LPS) scheme is suggested to solve the proposed problem. Moreover, to restrict the upper limit of the chemo-drug dose based on the age of the patients a Mamdani fuzzy system is designed. Simulation results on three cases; i.e. young, middle-aged and old patients, show the efficiency of the proposed treatment strategy. In each case the dynamics of the system is modified by immunotherapy, and then chemotherapy guides the trajectory of the system toward the tumor-free equilibrium point. After stopping the treatment, the trajectory of the system converges to this point due to the correction in the dynamics of the system.