What is thyroid cancer? – Kira Specialist

The thyroid is a butterfly-shaped gland located at the front of our neck. Thyroid cancer, a malignant tumor that develops from the cells of the thyroid gland.

What types of thyroid cancer are classified

The World Health Organization (WHO) classifies thyroid cancer into four categories:

Papillary thyroid carcinoma (PTC)
Papillary thyroid carcinoma (PTC)
follicular thyroid carcinoma (FTC)

Medullary thyroid cancer (MTC)

anaplastic thyroid cancer (ATC)

These four categories cover more than 95% of all thyroid cancers. Of these, papillary and follicular carcinomas are together called differentiated thyroid cancer.

Related reading:

Different types of thyroid cancer have different characteristics, as detailed in the table below

Table 1. Characteristics of the four major types of thyroid cancer
Type	Percentage	Population with good prevalence	Clinical features	Outcome
Papillary carcinoma	About 80%	20 to 40 years old, more common in women	There are usually no obvious symptoms in the early stages, but hoarseness and dyspnea may occur in the later stages	Lower malignancy, 10-year survival rate of 90%, easy recurrence
Follicular carcinoma	10% to 15%	around age 50	Usually asymptomatic nodules, which can present later with symptoms such as hoarseness and dyspnea	Moderately malignant, the prognosis is not as good as for papillary carcinoma, with 10-year survival rates of 98%, 88%, and 56% for patients in the low-, intermediate-, and high-risk groups, respectively.
Medullary carcinoma of the thyroid	5%	Any age, common between 50 and 60 years, similar proportion of men and women	Neck lumps, facial flushing, palpitations, diarrhea, and wasting	Moderate malignancy, with 10-year survival rates averaging 50% to 90%.
Undifferentiated carcinoma of the thyroid	5 % or so	around 70 years old	presenting with a rapidly growing mass in the neck with local compression symptoms such as dyspnea, dysphagia, hoarseness	Highly malignant, with a one-year survival rate of 5% to 15%.

Recognizing rare thyroid cancers

In addition to the four common types mentioned above, thyroid cancer includes many rare types, and their characteristics are summarized in the table below.

Table 2. Characteristics of rare types of thyroid cancer
type	Population	Clinical features	Outcome
Hürthle cell carcinoma	Female and over 50 years	More aggressive and more likely to metastasize distantly	Poorer
Primary squamous cell carcinoma of the thyroid	Elderly, more commonly in women	Tumor is rapidly enlarging, with significant signs of compression, and lymph node metastases may occur	Highly malignant, aggressive, poor outcome, 5-year survival rate less than 50%
Mixed medullary-filtrating carcinoma of the thyroid	Similar to medullary carcinoma, occurring at any age and in similar proportions in men and women	Lymph node and distant metastases, along with elevated blood calcitonin levels	Moderate malignancy with 10-year survival rates averaging over 50% to 90%
Primary mucinous epidermoid carcinoma of the thyroid	Female	Early presentation is mostly asymptomatic thyroid nodules, with corresponding presentation in later stages due to external invasion and compression.	Low malignancy, with a 5-year survival rate of nearly 90%
Intra-thyroidal thymic carcinoma	Middle-aged and elderly	Longer, slower progressive disease, often presenting as a painless nodule followed by symptoms such as tracheal compression or hoarseness	Better outcome
Sclerosing mucinous epidermoid carcinoma with eosinophilia	Adults, more common in women	Progressively enlarging neck mass with a tendency to extrathyroidal invasion	About half of patients have a disease-free survival of 3 months to 9 years, and half have local recurrence or distant metastases
Primary mucinous thyroid cancer	Unclear	High incidence of lymph node metastasis, susceptible to distant metastases, and rapid progression	Poor outcome
Note: Calcitonin (CT) is a common blood marker used to detect and follow up medullary carcinoma.

Co-written by Dr. Tingting Zhang, Cancer Hospital of Fudan University