Types of Thyroid Cancer - An Update 2026

WHO Tumour Classification 5th Edition 2022 has introduced changes that alter some of the nomenclature previously used for follicular cell derived thyroid tumours. I will outline these changes here and add to a previously published article I had on this site.

Types of Thyroid Cancer an Update 2026

There are several different types of thyroid cancers and they are broadly broken into categories based on the cells that they originate from and their behaviour. Most thyroid cancers are low grade, differentiated thyroid cancers that originate from thyroid follicle cells, generally behave in an indolent fashion and have very high rates of survival. At the other end of the spectrum are anaplastic thyroid cancers that are among the most aggressive human cancers, have a rapidly progressive disease course and have  rates of disease specific death approaching 100%. In between these are a group of poorly differentiated cancers that also originate from thyroid follicular cells, occur in older patients and do worse than differentiated thyroid cancer surgery. Finally, there is medullary thyroid cancer, a neuroendocrine tumour of parafollicular c cell origin that just happens to occur in the thyroid gland but is not of thyroid cell origin.

We now understand quite a lot about the molecular pathways involved in the development of thyroid cancers and this has helped to classify variants of these tumours and also helped to identify therapeutic strategies in cancers that are beyond surgical treatment. The mainstay of treatment of thyroid cancer however, remains surgery and the vast majority of thyroid cancers are cured with this and sometimes the use of I131.

Differentiated Thyroid Cancer

Papillary Thyroid Cancer (No real change here in the latest edition)

Papillary thyroid cancer (PTC) is the most common thyroid malignancy making up 75-80% of all thyroid cancers. It occurs in woman 4 x more frequently than men and is predominantly a tumour of adulthood in the child bearing age group but it does occur in children. 67% present with a thyroid nodule, 13 % present with a nodule and lymph nodes and 20% present with lymph nodes alone.

Lymph nodes can be small and can undergo cystic change and be mistaken for branchial cleft cysts. Occult micropapillary cancers occur in 6% of the population and are present at autopsy. There are a number of variants of PTC some of which have behaviour similar to or better than classic variant PTC like Follicular Variant , Encapsulated Variant, Cribriform-morular variant and Diffuse Sclerosing variant. Some have worse behaviour and generally occur in older patients such as Tall Cell Variant, Columnar Cell Variant, Hobnail Cell Variant and Solid and Trabecular Variant PTC.

Folliular Thyroid Cancer (No change in the 5th Edition)

Follicular thyroid cancer (FTC) is the next most common making up 6-10% of all thyroid cancers. 75% occur in women and age incidence peaks at 40-60 years. Iodine deficiency and radiation exposure are risk factors. Most present with a thyroid nodule and lymph node involvement is uncommon but up to 69% develop distant metastases to lung and bone.

There are 3 main types of FTC: Minimally Invasive FTC with a very good long term prognosis, Encaspulated Angioinvasive FTC which does worse and Widely Invasive FTC with a high distant metastatic rate and 50% longterm mortality.

Oncocytic Thyroid Carcinoma (Previously Hurthle Cell Cancer)

Oncocytic Thyroid Carcinoma and is now considered a separate entity to follicular thyroid cancer whereas it was previously considered a variant of follicular thyroid cancer with >75% oncocytic cells. The oncocytic cells are packed with abnormal mitochondria. These tumours are most common in older men ( mean age 57yrs). Hurthle cell cancers are more aggressive than follicular cancers with more extrathyroid extension, more metastases to lymph nodes and higher rates of distant metastases and mortality.

The different histopathological features and molecular profile set it apart from follicular carcinoma, although there are 3 types similarly named to the types of follicular thyroid cancer 1. minimally invasive, 2. encapsulated angioinvasive and 3. widely invasive. Patients with the latter being the most aggressive particulary when >4cm in size and in older patients.

Poorly Differentiated Thyroid Cancer (Changes in the WHO 5th Edition)

This is a malignancy of Follicular cell origin that makes up 0.3-7% of all thyroid cancers. It occurs in older patients and usually presents as a large, solid and often rapidly growing thyroid mass. There is a high rate of nodal and haematogenous metastases and a 3 yr survival rate of around 35%.

It has behaviour that sits between differentiated thyroid cancer and anaplastic cancer and can originate de novo or from a differentiated thyroid cancer or goitre and can under go a series of mutations to de-differentiate. There are solid and trabecular variants and these cell pattern types can be mixed. Tumours must also demonstrate tumour necrosis, a high mitotic rate and or convoluted nuclei.

In the WHO 5th edition for diagnosis:

It must now have 5 characteristics for diagnosis

• Solid/trabecular architecture

• Absence of nuclear features of papillary thyroid carcinoma

• Tumor necrosis

• Mitotic index ≥3/10 high power fields (HPFs)

• And/or convoluted tumor nuclei.

  
  

It has worse behaviour than DHGTC as below but still behaves better than anaplastic cancer and it has It has a 5 year survival of 62%.

Differentiated High Grade Thyroid Cancer (New in the WHO 5th Edition)

This is a new entity in the 5th edition WHO Classification defined as having differentiated features (like papillary or follicular) alongside either one of two high-grade characteristics specifically > 5mitoses per mm2 or tumour necrosis, it acts as an intermediate between well-differentiated and anaplastic thyroid cancer. It differs from poorly differentiated thyroid cancer in that it retains differentiated papillary or follicular features rather than losing these and becoming solid/trabecular. It has a 5 year survival of 62%.

Medullary Cancer (No change in WHO 5th Edition)

A neuroendocrine tumor derived from C cells  of the ultimobranchial body of the neural crest, which secrete calcitonin. Makes up  1 - 2% of thyroid carcinomas. 70% are  sporadic (nonhereditary) and 30% familial (hereditary). The sporadic tumours are solitary and peak in ages 40 - 60. The hereditary type occurs in  younger patients (mean age 35) and are usually bilateral and  multicentric with C cell hyperplasia. Familial MTC is due to MEN 2A or 2B syndromes, familial medullary thyroid carcinoma (FMTC) syndrome, von Hippel-Lindau disease or neurofibromatosis.

This is caused by gain of function germline mutations in the RET gene. Presents as a hard thyroid mass and up to 75% have nodal metastases. Serum calcitonin correlates with tumour burden and those with systemic metastases may have diarrhoea and flushing. 5 year survival is 65-90% and prognosis is worse with higher stage, nodal metastases, male, MEN2B, 918RET mutation, high mitotic activity and vascular invasion.

Anaplastic Cancer (No change in WHO 5th Edition)

Anaplastic thyroid cancer (ATC) is among the most aggressive and deadly human cancers. It usually occurs in older patients in their 8th and 9th decades. It makes up 2-5% of thyroid cancers but is responsible for 40% of thyroid cancer deaths. This tumour presents as a rapidly progressive large neck mass with invasion of central compartment structures associated symptoms of hoarseness, dyspnoea and dysphagia.

There are usually involved lymph nodes and 30-40% present with distant metastases. 50% have a prior multi nodular goitre and 20% have a prior differentiated thyroid cancer and dedifferentiation occurs in this tumour with a high rate of TP53 mutation. 1 year survival is in the 10-20% range. Patients do better if they can have surgical resection of their disease although many patients present with disease that has advanced beyond resectability.

Frequently Asked Questions

What is the most common type of thyroid cancer, and is it dangerous?

Papillary thyroid cancer is the most common type, making up 75-80% of cases. And the reassuring part is that it's usually not very dangerous. It grows slowly, and most people are cured with surgery alone, sometimes with radioactive iodine afterwards.

What is the deadliest form of Thyroid Cancer?

Anaplastic thyroid cancer is dangerous because it grows and spreads rapidly, often invading nearby structures such as the windpipe, oesophagus, and larynx. It can also spread to distant organs early and is difficult to treat because the cancer cells are poorly differentiated. 

Why is Anaplastic Thyroid Cancer dangerous?

• It's always Stage IV at diagnosis, regardless of tumour size, because it's already spread by the time it's found.

• Cells lose their thyroid identity, which also makes radioactive iodine, the go-to treatment for other thyroid cancers, useless here.

• Invades nearby structures fast

• Frequently spreads silently to the lungs or other organs before diagnosis.

• Resistant to standard treatment, so chemo and radioactive iodine have limited effect.

• Very short survival window

What is differentiated high-grade thyroid cancer?

Differentiated high-grade thyroid cancer is a type of thyroid cancer that retains the features of differentiated papillary or follicular cancer but shows high-grade features, such as increased mitotic activity or tumour necrosis. It behaves more aggressively than typical differentiated thyroid cancer but generally less aggressively than anaplastic thyroid cancer.

Who is most likely to get Thyroid Cancer?

• The risk varies depending on the type of thyroid cancer. 

• Papillary thyroid cancer is about four times more common in women and typically affects adults, although it can occur in children. 

• Follicular thyroid cancer also occurs more often in women and is most common between ages 40 and 60. 

• Oncocytic thyroid cancer tends to affect older adults, particularly men. 

• Sporadic medullary thyroid cancer commonly occurs between 40 and 60, while hereditary forms tend to develop earlier. 

• Anaplastic thyroid cancer mainly affects older adults, usually in their 70s and 80s.

Can a Thyroid Cancer come back after treatment?

Yes, thyroid cancer can come back after treatment, even with the more treatable types. Papillary thyroid cancer has an excellent overall outlook but can recur years or even decades later, particularly when lymph nodes are involved or the tumour has higher-risk features. Regular follow-up with blood tests and imaging helps detect recurrence early.