Most thyroid cancers are slow growing tumors and generally carry a favorable prognosis.
However, some thyroid cancers are quite aggressive and carry a poor prognosis. One dangerously aggressive form of thyroid cancer is called medullary thyroid cancer which is usually familial. A thyroid cancer is usually discovered as a result of a fine needle aspiration biopsy or the surgical biopsy of a thyroid nodule. It destroys any remaining thyroid cells, cancerous as well as non-cancerous. Thus, measuring serum thyroglobulin becomes an excellent tool to detect the recurrence of thyroid cancer, indicated by an increase in thyroglobulin level.