Good question! I want to know this, too. My RAI is on Thursday, my scan is a week after to see how much cancer is left and where it is. They found it in 3 lymph nodes in surgery so does that mean it can travel to other places? Is that common?
They usually do a whole body scan to make sure there is no spread anywhere else---when they do that scan differs from place to place.
Do not bother to look at the screens when you have the scans done, they will scare you needlessly.....the radioiodine collects in certain places (ie, bladder), and only the doctors can determine if it's a spread or not.
If pappillary spreads, it's usually limited to the neck. No matter where it spreads, it can be killed with RAI, so don't worry.
I don't believe thyroid cancer mutates into any other cancer. It rarely "metastisizes"---spreads beyond the thyroid, but if it does spread, pappillary would usually go to the neck (ie, lymph nodes, muscles near the thyroid). There have been members on here that actually found the follicular thyroid cancer because a rib broke, and it was biopsied and was thyroid cancer. Follicular could go to bone, and even more rarely, lungs.
Like I said, even if it does spread beyond the thyroid, it is usually destoyed with RAI. My surgeon said to me that statistically, people who get thyroid cancer outlive a sibling that did not have thyroid cancer. It is very curable, and you don't have to worry at this time about worst case scenarios, because statistically, it's just not a cancer that kills people.