I agree, yes you are in shock and yes it does stuff up your life and plans, but I also agree you can get Married anywhere, that's not what's important. You cannot get married and live a wonderful life together with the ones you love if you don't take care of number 1, YOU, first!
Do what has to be done, then pick up the pieces. Your family and friends will understand. It would be a shame to miss your holiday but you may not enjoy it anyway if you are worrying all the time???
I hope you get some answrers soon on treatment so you can plan around them. Good luck with your journey XXXX