Here's another passage from The Hobbit, this one sounding as though it refers directly to chemotherapy:
"Don't stray off the track!--if you do, it is a thousand to one you will never find it again and never get out of Mirkwood; and then I don't suppose I, or anyone else, will ever see you again."
"Do we really have to go through?" groaned the hobbit.
"Yes, you do!" said the wizard, "if you want to get to the other side."
And here's one more, which represents nicely the triumphant feeling of the patient who has successfully finished treatment:
There was the usual dim grey light of the forest-day about him when he came to his senses. The spider lay dead beside him, and his sword-blade was stained black. Somehow the killing of the giant spider . . . made a great difference to Mr. Baggins. He felt a different person, and much fiercer and bolder in spite of an empty stomach, as he wiped his sword on the grass and put it back into its sheath.
"I will give you a name," he said to it, "and I shall call you Sting."