First of all, I think you need to know that benign means good. Malignant means bad. Most,not all, but most nodules are benign. A nodule can grow slowly or can grow fast. If the doc didn't notice it 2 years ago then it probably was just an itty bitty nodule and has grown over time. Nodules which have grown fast (in a few months) can be a worry. Again that is not always the case.
Thyroids are a law unto themselves and really do not follow a black and white text book pattern of behaviour. Which is just as frustrating for doctors as well as patients!
Just because the specialists field is cancer is not to say you have it. Often docs send you to who they think is the best in their body bit!
You will probably more than likely have to have a biopsy, which will give a very good idea of what is going on. It could be a cyst, which is easily drained, it could be a solid one with no need for any thing to be done, but if it got bigger in the future surgery would probably be the option. If it is a cancer then in a silly way of saying it, thyroid cancer is the best cancer to get. It is treatable and although the other forum users who are being treated right now would say it isn't fun, it is often a much better result long term than most other cancers.
It's normal and ok to be petrified! I was too! I think we all get that way. But do take a big breath, learn as much as you can, so you are fore-armed...you will then be able to understand what is happening to you and feel more in charge, which will make you feel less worried.
I hope all that gives you some peace of mind.
I can tell you from experience that huge does not necessarily mean malignant. My tumor was more than three inches long - about the size of a small tangerine. I had half my thyroid removed two months ago. It was completely benign.
Just take things one day at a time. And keep copies of all your test results. You never know when you may need them.