Cancer is one of the most fatal disease as well as its very painful too but early diagnosis of your disease can prevent you a lot from danger so cancer should be caught when it is benign....but patient will power is also very important...I wish that may your wife get well soon...
Moving towards topic you are also saying like me that IV is most suitable route for quick relief of pain as you have given a real example of your wife that she first takes pills that have slow action on body but now with injections that's all fine...

Good luck with engagement challenge