Types of Thyroid Cancer

June 15, 2024 
This page was reviewed under our medical and editorial policy by Sasan Fazeli, M.D., assistant clinical professor in the Department of Diabetes, Endocrinology and Metabolism, and Karen Tsai, M.D., assistant clinical professor in the Department of Diabetes, Endocrinology and Metabolism, City of Hope^® Cancer Center Duarte.

During the thyroid cancer diagnosis process, the care team may diagnose a thyroid cancer type based on the specific cells affected.

Thyroid cancers mainly affect one of two types of cells in the gland — follicular cells and parafollicular cells (also called C cells). Follicular cells are those that produce thyroid hormones. C cells produce calcitonin, a hormone that helps regulate calcium levels in the blood by lowering it.

The majority of thyroid cancers start from follicular cells. Medullary thyroid carcinoma is the only type of thyroid cancer that develops from C cells.

Common Thyroid Cancer Types

Thyroid nodules are lumps or bumps that form in the thyroid gland. While most are not harmful, 10% to 15% may be cancerous.

Each cancer differs in how quickly it grows and spreads. The appearance of these cancers may be described as well-differentiated or poorly differentiated. Under a microscope, well-differentiated cells look much more like normal cells, while poorly differentiated cells do not.

Cancers with the more normal, well-differentiated cells tend to have better outcomes than those with more abnormal, poorly differentiated cells. The cells of papillary and follicular thyroid cancer are considered differentiated.

Papillary Thyroid Cancer

Papillary thyroid cancer is, by far, the most common thyroid cancer, making up 80% of these tumors. It tends to grow slowly in one lobe of the thyroid gland. It may also move into nearby lymph nodes. Even when it spreads, this type of cancer is often treated successfully.

Follicular Thyroid Cancer

Follicular thyroid cancer is the second-most common type, accounting for 10% of thyroid cancers. The treatment outlook is good for most cases. This type of cancer usually does not spread to lymph nodes, but it may spread to other parts of the body, such as the lungs or bones.

Less Common Types of Thyroid Cancer

Less common thyroid cancer types are listed below.

Medullary Thyroid Cancer

Medullary thyroid carcinoma (MTC) accounts for about 3% of thyroid cancers. It is non-differentiated, meaning it tends to be more difficult to address. It may be controlled if it is treated before it spreads to other areas, such as the lymph nodes, lungs, liver or bone. However, MTC sometimes spreads before a thyroid nodule is found.

Anaplastic Thyroid Cancer

Anaplastic thyroid cancer (also called undifferentiated carcinoma) makes up 2% of thyroid cancers. It often spreads quickly beyond the thyroid gland, and it may be very hard to treat.

Poorly Differentiated Thyroid Cancer

Poorly differentiated thyroid cancer (PDTC) is rare, representing about 2% of thyroid cancers in the United States, according to a 2019 review in the journal Thyroid. It is much more difficult to treat once it has spread beyond the thyroid gland compared to when it is detected earlier.

Oncocytic (Formerly Called Hürthle Cell) Thyroid Cancer

Oncocytic thyroid cancer is also known as Hürthle cell thyroid cancer (HCC). It is a rare type of follicular cancer, making up 3% of thyroid cancers. Oncocytic thyroid cancer is differentiated, meaning the cells appear close to normal, but it is aggressive, and it’s much more likely to be larger and spread compared to other follicular thyroid cancers.

Metastatic Thyroid Cancer

Metastatic thyroid cancer is cancer that has spread beyond the thyroid gland. The cancer may spread locally to the lymph nodes of the neck and to more distant parts of the body, such as the lungs and bones. Most thyroid cancers are caught early and treated successfully, but medullary and anaplastic thyroid cancers are the most likely to metastasize, and therefore, more challenging to treat.

Thyroid Cancer Recurrence

It is very important for patients who complete cancer treatment to continue close monitoring with the thyroid cancer care team and continue active surveillance. For some, the cancer does not go away completely, and regular thyroid cancer treatments may be needed to keep it under control.

Even if tests show no evidence of cancer, there is a chance it may return. Thyroid tumors may grow slowly and return 10 to 20 years after treatment.