Is it possible for a thyroid cancer to metastasize into only one part of the body?

Yes: There are many different types of thyroid cancer. The most common one is papillary thyroid cancer. This type is slow growing and typically does not "spread." if it does, it typically will spread to the lymph nodes, but other sites are also possible.

Yes: The most common site for thyroid cancer to metastasize is to the lymph nodes in the neck near the thyroid. In many cases, this is the only site of metastases and it can be cured with surgery (and usually radio iodine).

Sort of: When a tumor metastasizes, it usually seeds multiple organs in the body. Not all of the seeded sites may develop obvious metastases, so it may appear that only one site, the one with a large tumor, is involved, but many other sites are likely to have sub-clinical metastases.

Yes: Often well-differentiated thyroid cancer will only go to neck lymph nodes, this is then removed and radioactive iodine treatment is given. Most of the time the patient's prognosis continues to be excellent. If it has metastasized to multiple areas or cannot be resected, then radioactive iodine may be the only option. Prognosis is still good with well-different. Thyroid cancer in that situation.