This paper studies chaotic behavior in cancer dynamics when a treatment procedure is introduced. Recently introduced virotherapy is considered for the cancer treatment. Chaotic behaviors are investigated by using the Lyapunov Exponent for a set of parameters. The chaotic behavior is studied by using the mathematical model of the cancer dynamics involving the virotherapy. Through simulations and the Lyapunov Exponent, it is proven that recently introduced virotherapy exhibits chaotic behavior. The results indicate that virotherapy may result in re-growth of the tumor due to chaotic nature of the treatment.