I have had surgery and received treatment for stage 3 ovarian for 3+ years. My oncologist told me the same thing, not to take mega doses of vitamins as they might interfere with treatment. No clear explanation. Since I have researched and uncovered enough to suggest otherwise I attempted to find an oncologist more open to alternative/complementary treatments. They don't exist in my area. The only answer I can find is they are not licensed to practice other methods of treatment and strictly follow AMA guidelines. I also take Essiac. All the Dr. had to say was if you think it helps then take it. I'm looking for answers too. Good luck.