Thyroid cancer is a malignant (cancerous) growth in the thyroid gland. The thyroid is a butterfly-shaped gland in your neck that helps regulate your body’s metabolism. Cancer of the thyroid occurs more often in people who have undergone radiation to the head, neck, or chest. It is more common in women than in men. A family history of thyroid cancer is also a risk factor. Thyroid cancer usually appears as small growths (nodules) within the thyroid gland. Most thyroid cancers don’t cause any symptoms, but you should see your doctor if you notice a lump or swelling in your neck. Your doctor may perform a thyroid scan, an ultrasound, blood tests, or a biopsy—the removal of a tissue sample for examination under a microscope—to check for cancer. There are four major types of thyroid cancer. Papillary thyroid cancer is the most common and least dangerous form. It accounts for about 80% of all cases, and affects more women than men. Treatment for papillary thyroid cancer usually involves surgery to remove part or all of the thyroid (called a thyroidectomy), thyroid hormone therapy, and using radioactive iodine to destroy any remaining cancer cells after the thyroid is removed. Follicular thyroid cancer occurs most often among those who are 20 to 60 years old and accounts for about 15% of thyroid cancer cases. This type grows slowly and can be treated successfully if caught early. Treatment for follicular thyroid cancer may include thyroidectomy and radioactive iodine therapy. Medullary thyroid cancer tends to spread through the lymphatic system and the bloodstream to other parts of the body. It accounts for about 3% of all thyroid cancers. Medullary thyroid cancer is associated with other inherited cancer syndromes. This tumor produces excessive amounts of calcitonin, a hormone that regulates the amount of calcium in the blood. This slow-growing cancer is easier to control if detected and treated before spreading to other parts of the body. Treatment may include thyroidectomy; additional surgery may be necessary if the cancer has spread. Anaplastic thyroid cancer tends to occur most often in people older than 60 and accounts for less than 2% of thyroid cancer cases. This rare, quick-growing cancer spreads to other parts of the body and is very difficult to treat. Many people diagnosed with anaplastic thyroid cancer may die within six months of diagnosis. Treatment for anaplastic thyroid cancer may include thyroidectomy, radiation therapy, and anticancer drugs.