There are several forms of thyroid cancers which are staged in different ways. The commonest form of thyroid cancer
are the well differentiated thyroid cancers know as papillary or follicular thyroid cancers.
Unlike most other cancers, differentiated thyroid cancers(DTC) are not staged before treatment. The staging of DTC is done after thyroid and neck surgeries. The staging is done by a radioactive tracer called Radio-Active-Iodine(RAI). Thyroid cells, including thyroid cancer cells, actively take in Iodine in the blood stream. When a patient is fed with RAI, this allows the tracer to seek out thyroid cancer cells anywhere in the body. This is by far the most accurate way of looking for spread of DTC. If the patient has not had a near complete thyroid removal, the RAI will congregate in the normal thyroid tissue and thus the RAI scan will not be helpful. Staging therefore can only take place only after thyroid removal.
The other types of thyroid cancer are Medullary Thyroid Cancer(MTC) and Anaplastic Thyroid cancer(ATC).
MTC is actually from parafollicular C cells embedded in thyroid gland and they produce a protein Calcitonin that can be used to measure active disease. The natural course of MTC is usually indolent although it can spread to the liver and lung. RAI and PET scans have not been found to be helpful for detecting spread. Normal CT are the recommended staging tools.
ATC is a unfortunate lethal condition that usually spread aggressively from the thyroid to the surrounding tissues in months. The average survivor period is between 6-12 months. Staging using a PET scan is sometimes helpful.