“…In literature, applications of optimal control theory to mathematical models of cancer biology and role of chemotherapy began to appear in the 1980s and have appeared with regularity in the following years to the present day. The reader can refer to some of these works, such as for example (Swan, 1980 , 1988 , 1990 ; Martin, 1992 ; Swierniak et al, 1996 ; Kimmel and Swierniak, 2005 ; Pillis et al, 2008 ; Collins et al, 2010 ; Batmani and Khaloozadeh, 2011 ; Ledzewicz et al, 2013 ; Ghaffari et al, 2014 ; Michor and Beal, 2015 ; Wang and Schättler, 2016 ; Carrère, 2017 ; Irurzun-Arana et al, 2018 ). Indeed, a tumor undergoing pharmacological treatment can be viewed as a control system with the state of the system, given by the number of cancer cells at time t , N ( t ), and the control input at time t , u ( t ).…”