Thyroid cancer is a cancerous tumor or growth within the thyroid gland. The thyroid gland is located in the front of the neck, under the thyroid cartilage (Adam’s apple). It is part of the endocrine system, a network of glands that produce and secrete hormones. It is responsible for absorbing iodine from food, water and the blood and using the iodine to produce thyroid hormones. Thyroid hormones play a major role in regulating the body’s metabolism, the body’s process of using food for energy and growth.

The thyroid gland has two halves – the left lobe and the right lobe. Usually, the thyroid gland cannot be felt despite being just underneath the skin.

The thyroid gland contains several types of cells and different cancers can develop from each type of cell. Thyroid follicle cells  manufacture and store thyroid hormone. They also produce thyroglobulin, a type of thyroid protein. C cells produce a hormone called calcitonin. These different cells can produce different types of thyroid tumors. These tumors can be either benign (noncancerous) or malignant (cancerous).

Most growths found in the thyroid are benign nodules, growths that develop from follicle cells. They can be found in normal-sized thyroid glands and enlarged thyroid glands (goiters). The thyroid may contain one nodule or multiple nodules. An enlarged thyroid gland with multiple benign nodules is known as a multinodular goiter. Frequently, these nodules are fluid-filled cysts, or lumps of stored thyroid hormone known as colloid nodules. While some types of benign thyroid nodules may be related to other medical conditions, such as hyperthyroidism, they are not cancerous. The exact cause of most benign thyroid nodules is unknown.

Malignant thyroid tumors can develop from either type of thyroid cell. Because the thyroid gland is located just under the skin, tumors are often able to be felt as bumps in the neck. According to the American Cancer Society (ACS), one-third of all people develop thyroid nodules. They can occur at any age, but are most common in adults. Often, people discover these bumps on their own by seeing or feeling them. In some situations, the nodules remain undiscovered and never cause a problem.