This page was reviewed under our medical and editorial policy by
Maurie Markman, MD, President, Medicine & Science
This page was updated on June 7, 2022.
The types of thyroid cancer are classified based on how similar they look to normal thyroid cells under a microscope (differentiated vs. undifferentiated) and by the type of cell from which they develop. The four primary types of thyroid cancer are follicular, papillary, anaplastic and medullary.
Papillary thyroid cancer, or papillary carcinoma, is the most common type of thyroid cancer, accounting for approximately 80 percent to 85 percent of cases. Papillary carcinomas are slow-growing, differentiated cancers that develop from follicular cells and in one or both lobes of the thyroid gland.
This type of cancer may spread (metastasize) to nearby lymph nodes in the neck, but with a comprehensive thyroid cancer treatment plan, a patient may have a good prognosis (outlook for survival).
Follicular thyroid cancer, or follicular carcinoma, is the second most common type of thyroid cancer. It is found more frequently in countries with an inadequate dietary intake of iodine. Follicular carcinoma is also a differentiated form of thyroid cancer.
In most cases, treatment offers patients a good prognosis, although it is somewhat more aggressive than papillary cancer. Follicular carcinomas do not usually spread to nearby lymph nodes, but they are more likely than papillary cancers to spread to other organs, like the lungs or the bones.
Hürthle cell thyroid cancer, also known as Hürthle cell carcinoma and oxyphil cell carcinoma, is a rare thyroid cancer. This subtype of follicular carcinoma accounts for fewer than 5 percent of all thyroid cancers.
Medullary thyroid cancer, or medullary thyroid carcinoma, develops from C-cells in the thyroid gland, and is more aggressive and less differentiated than papillary or follicular cancers. Approximately 4 percent to 10 percent of all thyroid cancers are of the medullary subtype.
These cancers are more likely to spread to lymph nodes and other organs, compared with the more differentiated thyroid cancers. They also frequently release high levels calcitonin and carcinoembryonic antigen (CEA), which may be detected by blood tests during the thyroid cancer diagnosis process.
Anaplastic thyroid cancer, or anaplastic thyroid carcinoma, is the most undifferentiated type of thyroid cancer, meaning that it looks the least like normal cells of the thyroid gland. It is a very aggressive form of cancer that quickly spreads to other parts of the neck and body. It's a rare thyroid cancer that occurs in approximately 2 percent to 3 percent of thyroid cancer cases.
When the care team is evaluating thyroid cells to determine whether cancer is present, they classify the cells based on how different they look from normal thyroid cells to determine which of the following classifications they fit.
Cells that are well-differentiated make up the majority of thyroid cancer diagnoses, and these have the best prognosis among the differentiations.
When cancer cells are poorly differentiated, they have more abnormalities compared to healthy thyroid cells. Poorly differentiated thyroid cancers represent between 3 percent and 5 percent of all thyroid cancers, making this classification more rare.
When thyroid cancer cells don’t look like normal thyroid cells, they may be classified as undifferentiated, which are considered more challenging to treat than differentiated and poorly-differentiated thyroid cancers. These cancers are aggressive and rare, representing between 2 percent and 3 percent of all thyroid cancers.
Next topic: What are the stages of thyroid cancer?
