Types of TC
There are four main types of thyroid cancer: (1) Papillary thyroid cancer, (2) Follicular thyroid cancer, (3) medullary thyroid cancer, and (4) anaplastic thyroid cancer. Papillary thyroid cancer is the most common type and represents more than 90% of all thyroid cancers. There are multiple subtypes of papillary thyroid cancer that may have a better or worse prognosis than classical forms of papillary thyroid cancer. While the prognosis and follow-up of these various subtypes may vary slightly depending on the variant, the overall the treatment and management of these tumors is similar. Papillary, follicular and anaplastic thyroid cancer all arise from the normal thyroid follicular cell which makes thyroid hormone. Medullary thyroid cancers are different in that they arise from other neuroendocrine cells that live within the thyroid.
What is different about medullary thyroid cancer?
Except for medullary thyroid cancer, the other common types of other thyroid cancers arise from a thyroid follicular cell (the normal thyroid cell that concentrates iodine and produces/stores/releases thyroid hormone). Medullary thyroid cancer arises from a different cell type within the thyroid gland (c-cells). These c-cells are neuroendocrine cells that are very different from thyroid follicular cells in that they do not concentrate iodine and they do not make thyroid hormones.
Unlike the other thyroid cancers, medullary thyroid cancer may be part of a hereditary syndrome in which each first degree relative of an affected patient has a 50% chance of developing medullary thyroid cancer. The genetic mutation for hereditary thyroid cancer is now well know and its detection is possible with a commercially available blood test (RET proto-oncogene). Of all the patients with medullary thyroid cancer, only 25% have a genetic syndrome that can be passed through a family. The other 75% have sporadic medullary thyroid cancer that affects only that patient and is not hereditary.
Unlike papillary and follicular thyroid cancers with make thyroglobulin, medullary thyroid cancer makes tumors markers known as calcitonin and CEA (carinoembryonic antigen). In addition, the cells that give rise to medullary thyroid cancer are not sensitive to TSH, so thyroid hormone suppressive therapy is not needed. Rather, in medullary thyroid cancer the thyroid hormone levels are adjusted to achieve a TSH in the normal reference range.