Hi Ishyanna!
Welcome to the forum. I'm a little confused. Are you having problems on the thyroid in your neck and the thymus in your chest at the same time?

Thymus can grow back if tissue remains after removal, and I have a woman I work with that had a cancerous node on her thyroid that was removed and they keep checking to make sure that doesn't grow back. I suppose living tissue anywhere in the body can regrow if there is anything at all for it to start from.

I hope you get all the answers you need, and the proper treatment. You'll really enjoy our forum. Lots of wonderful and knowlegeable people. It's helped me a lot!