With enough money people can always find a doc who'd give the OK. I guess it was actually his own decision. They might tell him about the risks, the side effects, the slim chances of success - but if Sam still insists he'd wanna go forward with it, then they can't stop him. Sam's tweets, especially earlier this year, revealed a very determined, combative attitude towards his disease. And the fact that he & the earlier chemo rounds had seemed to fare much better than initially predicted could have fuelled his false hopes that he might even stand a chance against the cancer. Now he might be resigned to his fate (though I'm not sure), but if he wants to prolong his life as much as possible, he has to pursue an aggressive course of treatment since the cancer should become more and more resistant to chemo and affect more and more organs.
So basically you're saying:
Cancer's gonna cance.