The thyroid gland is a small two-lobe endocrine gland in the shape of a butterfly that is located in the front, lower portion of the neck, below the larynx (the voice box or Adam’s apple). The thyroid gland is made up of three parts, the follicles, follicular cells, and the parafollicular cells. Follicles are tiny, spherical groups of cells that contain the proteins used to create the thyroid hormone. The follicles are surrounded by a single layer of follicular cells. Parafollicular cells are randomly distributed among the follicular cells and the spaces between the spherical follicles.

The gland secretes three hormones – calcitonin (or thyrocalcitonin) from the parafollicular cells (also known as C-cells, triiodothyronine (T3) and thyroxine (T4). While calcitonin plays a significant role in reducing excess calcium in the blood, the two thyroid hormones affect three functions in the body. They increase the metabolic rate, thereby affecting appetite, food absorption in the stomach, nutrient uptake in the cells, the breakdown of fats, and glucose breakdown. These hormones trigger the increase in heart and breathing rate, thereby increasing blood flow and the body’s temperature. They also play an important part in the development of the brain in the fetus and the early part of a child’s life. Other functions include maintaining thought patterns, sleep, and normal sexual function.

Thyroid cancers are of two main types – differentiated and undifferentiated. Most of the thyroid cancers are differentiated and include the following:

• Papillary : This form accounts for about 80% of all thyroid cancers cases. It grows slowly and most often affects only one lobe of the thyroid gland. It grows in the follicles and often spreads to the nearby lymph nodes. It can occur at any age but is found commonly in people between the ages of 30 and 50 years. The chances of recovery are high. This type is also called papillary carcinoma or papillary adenocarcinoma.
• Follicular : The next common type of thyroid cancer is also called follicular carcinoma or follicular adenocarcinoma. It occurs in about 10% of all thyroid cancer cases. It tends to spread more to other parts of the body and less to the nearby lymph nodes. The chances of recovery are not as high as the papillary but are still encouraging.
• Hṻrthle cell : About 3% of thyroid cancers cases are of this type. It is a very elusive type – hard to find and treat.

There are two types of undifferentiated thyroid cancers:

• Medullary : Medullary thyroid cancer (MTC) occurs in about 4% of the cases. It affects the parafollicular or C-cells, often spreads to the lungs, liver and lymph nodes even before the tumor appears in the thyroid gland. It is very difficult to find and treat. There are two sub-types; sporadic MTC that occurs in 0.04% of all cases and is not hereditary; and familial MTC that is hereditary and occurs in about 3% of all cases.
• Anaplastic carcinoma : Also called undifferentiated carcinoma, it is a very rare type accounting for only 2% of all thyroid cancer cases. It spreads quickly to the neck and other parts of the body and is difficult to treat.
• Thyroid lymphoma : This is a rare type of thyroid cancer found in about 1%-2% of all cases.
• Sarcoma : This is an extremely rare form of thyroid cancer.