Re: Synthyroid and thyroid cancer
About 50% of the general population have thyroid nodules. So I'm not sure nodules are automatically cause for concern.
There are two issues with thyroid nodules:
1. "Hot Nodules" - these are nodules what secrete excess amounts of thyroid hormone. That doesn't sound too bad, except that they are not constant, and can cause large enough variation to make you swing from hypo to hyper.
2. "Cold Nodules" - there are the type, especially when the boundaries are well formed, that are under suspicion of cancer. In this case, a Fine Needle Aspiration Biopsy (FNAB) can be performed to determine if they are cancerous or not.
It isn't always necessary, but not a bad idea to have an ultrasound to have a better look at nodules. A somewhat definitive method is the uptake scan. However, that requires that you are off meds for a while, which isn't pleasant. There is controversy whether or not the uptake scan gives enough more useful information, over an ultrasound. It's been a while since I did my research, but I remember I determined that I would not have the uptake scan.
But to your question about T3. I haven't researched this directly, and maybe someone can answer more definitively. I would be pretty sure that T3 would only be supportive to the same goal as to why Doctors prescribe Synthroid for thyroid cancer. This is my logic:
Doctors prescribe Snythroid (and other synthetic T4-only medications, such as Levoxyl and Unithroid) to slow down your thyroid gland, or de-stimulate it. The thought is to keep the whole gland, including the cancerous part of it, as inactive as possible.
The mechanism that achieves this is as follows:
1. T4 med enters the digestive tracts
2. T4 med is absorbed through the intestine, into the blood stream as Total T4 (TT4)
3. Most of this T4 (99%+) is then bound to protein in the blood. What is left over is Free T4 (FT4).
4. Organs in the body (mostly the liver), then convert FT4 into Total T3 (TT3).
5. Most of this T3 (99%+) is then bound to protein in the blood. What is left over is Free T3 (FT3).
6. The Hypothalamus gland constantly monitors the blood for FT3. Upon finding more than enough FT3 in your blood, the Hypothalamus secretes Thyrotropin Releasing Hormone (TRH), telling the Pituitary to release more Thyroid Stimulating Hormone (TSH), telling the Thyroid gland to slow down.
So, you see, it is essentially FT3 that controls TSH, more-so than FT4 anyway. It is only logical that taking a medication with T3 in it, does support the same goal, of de-stimulating the Thyroid gland.
However, if all your mechanisms are working correctly... that is, your body readily converts FT4 into T3 ok, etc.... and you still have your Thyroid gland... then I think there is less risk in taking a T4-only medication. T4 meds raise your hormone levels slower than T3 meds. Also, Doctors are typically more familiar with T4-only meds.
Note, this completely disregards what med would be best to take for health reasons outside of Thyroid cancer, and to generally alleviate symptoms.
My opinions only, not medical advice. Always follow advice of your Doctor, not what I say here.