Types of Thyroid Cancer

There are 4 main types of thyroid cancer.

1.  Papillary

2.  Follicular

3.  Anaplastic

4.  Medullary

Less common types are thyroid lymphoma and thyroid sarcoma.

               Types of Thyroid Cancer -- Relative Frequency of Diagnosis

Ref: American Cancer Society (2010), National Cancer Institute (2010)

 

Differentiated

Papillary and Follicular are known as differentiated forms of thyroid cancer (DTC) or well-differentiated (WDTC). This means the mutated cancer cells still resemble healthy cells to some degree, and still have many of their qualities.  For example, similar to normal thyroid cells, differentiated thyroid cancer cells make use of iodine for their function.  Both forms of DTC develop in the follicular cells of the thyroid gland.

If Papillary thyroid cancer metastasizes (spreads), it travels via the lymphatic system and is therefore likely to be found in cervical (neck) lymph nodes. It is not uncommon for those with papillary thyroid cancer to have more than one cancerous nodule(s) in the thyroid gland and/or to have spread to lymph nodes in the neck and/or chest, at the time of diagnosis.

Although occurring very rarely, if Follicular thyroid cancer spreads, it travels via the blood system and is more likely to be found in the lungs or bones.

Some patients have a mix variant of Papillary-Follicular.

The vast majority of those diagnosed with thyroid cancer have one of the differentiated types (at least 90%). Those with differentiated disease have a very high rate of survival (99% survival, CCS 2009)

Papillary “Classic papillary thyroid carcinoma is formed of papillae with fibrovascular cores (H&E, original magnification _100).” Overview of Papillary Thyroid Carcinoma—Al-Brahim & Asa

 

Follicular “Follicular variant papillary thyroid carcinoma exhibits scallopingand hypereosinophilia of colloid (H&E, original magnification_100).” Overview of Papillary Thyroid Carcinoma—Al-Brahim & Asa

 

Variants & Poorly Differentiated

There are sub-variants to thyroid cancer including: Columnar, Tall Cell, Insular, Diffuse Sclerosis, and Hürthle Cell carcinoma (also known as Oxyphil Cell Carcinoma). These subtypes are very rare. In these types, the cancer cells are poorly differentiated and tend to grow and spread more quickly. The poorly differentiated variants make up about 2-4% of cases.

Anaplastic

Anaplastic carcinoma (ATC) is a very rare form of thyroid cancer. Although sharing some characteristics with papillary disease, it is thought to develop from an existing follicular cancer that further mutated, that is, became undifferentiated over time. It is believed that anaplastic cancers are likely long existing tumours that were left untreated and suddenly became aggressive. This form of cancer spreads rapidly and is much harder to treat. About 1.5% of cases are anaplastic.

Medullary

Unlike the differentiated forms of thyroid cancer which originate in the follicular cells of the thyroid gland, Medullary thyroid cancer (MTC) originates in the C cells of the thyroid gland.  This makes it a different disease from those described above, with different forms of treatment. This type of thyroid cancer makes the hormone calcitonin which helps control the amount of calcium in the blood. It also produces the protein carcinoembryonic antigen (CEA) which can be detected by blood tests.

There are two known types of medullary thyroid cancer.  The majority of people have the sporadic type (80%). This type is usually diagnosed in older adults and only in one lobe. The other type of MTC is familial (inherited).  The inherited type usually develops in childhood or early adulthood.  This type spreads more rapidly.  A blood test is available to test for the gene of familial MTC, and it is advisable that family members speak with a specialist to determine if they are a good candidate for this genetic testing.  Those who are known to carry the gene, often undertake a prophylactic total thyroidectomy surgery (surgery to remove the gland and help prevent the start of the cancer) as a precaution. Overall, about 4% of thyroid cancer is the MTC form. To get more information in regards to MTC, see Support for Medullary Patients.

Other forms

Thyroid Lymphoma is a cancer of the lymphatic system and Thyroid Sarcoma is a cancer of the thyroid supporting cells.  These cancers are very rare.  As these forms of thyroid cancer overlap more closely with lymphoma and sarcoma diseases, we recommend that people with these forms seek out resources made available by support groups for lymphomas and sarcomas.