There are four main types of thyroid cancer based on how the cancer cells appear under a microscope:
- Follicular thyroid cancer is cancer that forms in follicular cells in the thyroid. It grows slowly and is highly treatable.
- Papillary thyroid cancer is cancer that forms in follicular cells in the thyroid and grows in small finger-like shapes. It grows slowly, is more common in women than in men, and often occurs before age 45. It is the most common type of thyroid cancer.
- Medullary thyroid cancer is cancer that develops in C cells of the thyroid. The C cells make a hormone (calcitonin) that helps maintain a healthy level of calcium in the blood.
- Anaplastic thyroid cancer is a rare, aggressive type of thyroid cancer in which the malignant (cancer) cells look very different from normal thyroid cells.