Mark has been battling with kidney cancer for several years now.  His battles have included surgery, targeted therapy, and immunotherapy among others and he has traveled to many doctors around the US to gather the best information and give his best in the fight against kidney cancer, just as Nolan gave his best in this ascent of Citlaltépetl.  Mark’s wife is a doctor and that has helped them to navigate the complex US health care system (though it sometimes causes a little more worry because you know a little too much).