Firstly, I am not a doctor or medically trained so any advice that I give must be checked, double checked and verified. Think of it as something to research further.
I have read that d-limonene can have some positive effects against developing and spreading cancer. Therefore it might be worth you doing some quick research on that and then if it checks out, getting some as a preventative. It's not very expensive and can be found in citrus fruit peal and is extracted by steam distillation. It's in the essential oils of citrus fruits and also as a more pure form as a cleaner/degreaser. I do have some myself and have used it for other purposes internally. Get a dropper bottle if you order it. I cannot advise on the dosage required as I do not know. There is some research on pubmed.
There are other natural foods which have properties that can help. Chamomile tea(apigenin) is meant to have reduced risk of thyroid cancer and many other foods might be helpful.
Get a strong vitamin/mineral supplement, particularly selenium, such as Life Extension 2 per day capsules and take 3/day. Check out the different forms of selenium as some less common ones might be preferable in this situation.
Optimize Methylation as much as possible. Methyl group supplementation might be beneficial.