Thyroid Cancer

There are 4 main types of thyroid cancer: papillary, follicular, medullary, and anaplastic.  Papillary and follicular carcinomas are referred to as well differentiated thyroid carcinomas.  These cancers begin as nodules, and may spread to lymph nodes or other locations in the body.  The risk factors for thyroid cancer include radiation exposure (more than just a few X-rays), particularly at a young age, and family members with thyroid cancer.

Papillary Thyroid Carcinoma

Papillary thyroid carcinoma is the most common type of thyroid cancer, and fortunately it also has the best prognosis.  This type of thyroid cancer starts as a thyroid nodule, and sometimes spreads to the lymph nodes in the central neck (below the thyroid) or lateral neck (right side or left side).   The diagnosis is generally made through fine needle aspiration biopsy of either the thyroid nodule or occasionally a lymph node in the neck.  The small sample of cells can make the diagnosis because the nuclear features of the individual cells make the diagnosis.

Surgery is the primary treatment for this type of thyroid cancer, sometimes followed by radioactive iodine.  The initial surgery can be a thyroid lobectomy (removal of half of the thyroid) for low risk patients or a total thyroidectomy (removal of all of the thyroid).  If lymph nodes of the neck are involved or appear involved on evaluation with ultrasound, they should be biopsied and removed during the initial operation if they contain thyroid cancer.  Lymph nodes that don’t contain this thyroid cancer are best left in place.   Removal of lymph nodes that are not known to have cancer but have a small possibility of containing cancer is called an elective neck dissection.  While this is being studied, there is currently no scientific evidence to routinely support this practice for the treatment of papillary thyroid carcinoma.

Follicular Thyroid Carcinoma

Follicular thyroid carcinoma is the second most common type of thyroid cancer.  This type of thyroid cancer begins as a thyroid nodule, but generally does not spread to the adjacent lymph nodes.  However, it can spread to distant locations by way of the bloodstream.  The most common variant of follicular carcinoma  is known as Hurthle cell carcinoma.  The diagnosis of these types of cancer cannot be made by fine needle aspiration biopsy or frozen section analysis during surgery.  Surgical excision is the only way to determine benign lesions from cancer, as the pathologist must look at the capsule of the lesion once it has been excised and processed.

Surgery is also the primary treatment modality for this type of thyroid cancer, and consists of removal of half of the thyroid (lobectomy) or a total thyroidectomy, sometimes followed by radioactive iodine.  Lymph nodes are not involved anywhere near as often as they are with papillary thyroid carcinoma, so a neck dissection is rarely necessary.

Medullary Thyroid Carcinoma

Medullary thyroid carcinoma arises from cells in the thyroid called the parafollicular C-cells.  These cells secrete a hormone called calcitonin, which actually does very little in humans.  The majority of these cancers occur sporadically, but some are part of the multiple endocrine neoplasia (MEN) syndromes, specifically MEN 2A and 2B.  The diagnosis is usually made through fine needle aspiration biopsy of a suspicious thyroid nodule.   Testing for genetic mutations of MEN syndromes must be performed, because of the possibility of a tumor of the adrenal glands called a pheochromocytoma which can cause problems while undergoing anesthesia, the possibility of concurrent hyperparathyroidism, and to know if other family members need to be tested.  This type of tumor can be assessed by levels of calcitonin and carcinoembryonic antigen (CEA) in the blood.  These levels are drawn prior to surgery, and then used to monitor disease after the initial surgery.

As with all forms of thyroid cancer, it is important to assess the central and lateral neck for lymph node involvement.  This is either done through ultrasound or CT scan.

Surgery is the only treatment modality for this type of thyroid cancer.  The initial surgery is a total thyroidectomy, with  neck dissection to remove lymph nodes.   The minimum neck dissection is a central neck dissection, and frequently a lateral neck dissection if there is known involvement in the central neck.  Radioactive iodine is not administered for this type of tumor, and only in rare instances is external beam radiation recommended.

After surgery, levels of calcitonin and CEA are followed.  Unfortunately, this type of thyroid cancer has a higher propensity to recur in the lymph nodes of the neck or at distant sites such as the lungs.

Anaplastic Thyroid Carcinoma

This is the most dangerous type of thyroid cancer, and unfortunately it is nearly universally fatal within a year of diagnosis.  This type of cancer occurs as a differentiated thyroid cancer such as papillary or follicular thyroid carcinoma goes untreated and develops into this more aggressive form of thyroid cancer.  It subsequently grows rapidly, and invades any structures in its path.  Surgical debulking can be performed to relieve pressure put on the trachea or the esophagus, but complete removal of this tumor is rarely possible because of the extremely invasive growth pattern.  The disease has often spread to the lungs or other distant sites by the time the diagnosis is made.  The diagnosis can be made on fine needle aspiration biopsy.  Chemotherapy and radiation are often performed to slow growth of the tumor, but they are not curative.  Fortunately, this type of cancer is quite rare.