Thyroid Cancer
There are many types of tumors that can develop in the thyroid gland. Most of these tumors are benign, or noncancerous. Others are cancerous, which means they can spread into nearby tissues and to other parts of the body. Because the thyroid gland is close to the skin, tumors often appear as bumps in the neck. They are called thyroid nodules. Thyroid nodules can develop at any age, but they are most common in adults, occurring in one-third of all people. Often people find these bumps themselves by seeing or feeling them. Other times they are never noticed and never cause a problem.
Almost all (95 percent) thyroid nodules or tumors are benign. They develop from thyroid follicular cells and can be found in normal thyroid glands and goiters (enlarged thyroid glands).
Only a small fraction of thyroid nodules are cancerous (less than 5 percent). The most common type of thyroid cancer is a papillary carcinoma or papillary adenocarcinoma. Papillary cancers develop from the thyroid follicle cells and typically grow very slowly. Usually they occur in only one lobe of the thyroid gland, but in about 10 percent to 20 percent of the time both lobes are involved. Even though papillary cancer grows slowly, it often spreads early to the lymph nodes in the neck. Fortunately, nearly all people with papillary cancer do not die of this thyroid cancer.
The next most common type of thyroid cancer is called follicular cancer. Follicular cancer is much less common than papillary thyroid cancer. These cancers usually remain in the thyroid gland but can spread to other parts of the body, such as lungs and bone.The prognosis of follicular thyroid cancer is somewhat worse than that of papillary cancer. But most patients with follicular thyroid cancer do not die from it.
Doctors believe that in rare cases, existing papillary or follicular cancers can develop into a rare form of thyroid cancer called anaplastic carcinoma This is a very aggressive cancer that rapidly invades the neck and often spreads to other parts of the body. This cancer is nearly always fatal.
Medullary thyroid carcinoma (MTC) is the only thyroid cancer that develops from the C-cells of the thyroid gland. Sometimes this cancer can spread to lymph nodes, the lungs or liver even before a thyroid nodule has been discovered or a screening test has been done. These cancers usually make calcitonin and carcinoembryonic antigen (CEA). Calcitonin is a hormone also produced by normal cells that helps control the amount of calcium in blood. CEA is a protein produced by certain cancers, such as colorectal cancer and MTC. Both calcitonin and CEA are released into the blood and can be found by blood tests. Unlike papillary and follicular thyroid cancers, MTC does not produce thyroid hormone.
