off the top of my head:
cancer cells have distinctive traits that can be exploited for targeting [1]. A fairly elegant approach is to use a vesicle studded with antibodies to the tumor antigen to get the payload to the bad cells, the mRNA is then endocytosed into the tumor cell, expressed and the protien product adorns the tumor cell. when this is an antigen such one sees with measles there would be a long lasting immune response that would look for any cells with this antigen [i.e. target tumor cells]