Thyroid cancer is like skin cancer in terms of prognosis: most cases are mild and cured easily with surgery, while others are deadly. Approximately 85 percent of thyroid cancer patients are diagnosed with limited disease that requires only surgical removal. The remaining 15 percent have persistent, recurrent, or metastatic disease. The lungs are the most common site for metastases, followed by the bones.
Treatment options depend on the subtype. Reference 1 explains how thyroid cancer can arise by several different pathways. Thyroid tissue contains two main types of cells: follicular cells, which produce iodine-containing hormones, and C cells, which perform support services. There are several genetic mutations by which follicular cells can transform into papillary carcinoma. Different pathways lead to follicular carcinoma. Either of these cancer cell types can transform, by further genetic mutation, into anaplastic carcinoma. The C cell, on the other hand, can transform into medullary carcinoma. Papillary and follicular carcinomas are called “well differentiated”, and have the best overall prognosis. Medullary carcinoma is less common but more difficult to treat. Anaplastic carcinoma is rare, but is one of the most deadly cancers: the median survival time is less than one year.
After surgery, radioactive iodine can be used to kill well differentiated thyroid cancer cells. Thyroxine treatment is used to suppress thyroid stimulating hormone (TSH) production. This approach does not work for medullary and anaplastic carcinomas, because these cells do not take up iodine to produce the T3 and T4 hormones.
Chemotherapy and external beam radiation therapy are used in some patients, but their success rates are low. Current research is focused on targeted therapy drugs. These drugs are intended to disrupt the function of cancer cells specifically, while leaving healthy cells alone. Several of these have been approved for other cancers and are now being tested on thyroid cancer:
1. Sorafenib (Nexavar), approved for liver and kidney cancer
2. Sunitinib (Sutent), approved for kidney cancer and gastrointestinal stromal tumor