That person has just received some of the worst news of their lives, for no fault of their own. This is very relevant for approaching them with patience, kindness and care.
OP will need to reconcile their ambition and past expectations with being a decent human being and, possibly, a friend.
Cancer is bad, but without more details is imposible to know how bad it is. I've seen case in my family when they got a cancer, it was operated and got a minimal post treatment and lived happy ever after a few decades and counting, and other cases where it was too late and died like one year after the diagnosis. I had similar experiences with coworkers.
For example, in some prostate cancers the recomendation is to "do nothing", or to be more precice to wait and check them frecuently https://en.wikipedia.org/wiki/Active_surveillance_of_prostat... But in other cancers waiting is stupid and shoud be removed asap and get chemo and more.