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Difference Between Follicular Adenoma and Carcinoma

A follicular adenoma is a benign tumor of the thyroid that is entirely enclosed by the capsule. A carcinoma is a malignant tumor of the thyroid that invades the capsule. 

What is Follicular Adenoma


A follicular adenoma is a tumor that occurs in the thyroid gland but it is benign and is completely surrounded by the capsule of the thyroid.


Many patients with an adenoma of the thyroid gland do not show dysfunction of the gland, and only about 1% of those afflicted with the condition, do show hyperthyroidism. A single nodule is usually present on the thyroid gland with adenoma, which may or may not be felt. It can vary in size from about 1 to 10 cm, and often the person has no symptoms if the nodule is below 3 cm in size.


The diagnosis is based on cytology which means that the extent of invasion of the capsule needs to be ascertained through microscopy. The appearance of the cells of an adenoma is slightly different from that of a carcinoma of the thyroid, but it is often close in appearance which is why pathologists prefer to diagnose based on how much of the capsule is invaded, if at all. If the capsule is not invaded then the diagnosis is that of a follicular adenoma. Under the microscope, mitotic activity of cells is not evident and the cells are completely surrounded by the fibrous capsule. 


Follicular adenoma can be caused by a lack of iodine in the diet, and also by having a goiter. The Pax8-PPARγ fusion gene is expressed in some people who have adenoma, but less often when compared with carcinoma. 


The recommended treatment for follicular adenoma of the thyroid gland is surgical removal of the nodule. In many cases a part of the thyroid called the isthmus is where such a nodule is found and thus this is the section of tissue that the surgeon cuts out.

What is Carcinoma?


Thyroid carcinoma is a malignant tumor of the thyroid gland; the tumor is never enclosed by the capsule and rather actually invades the capsule.


The symptoms of the carcinoma only start to appear once the cancer has grown larger. A person often notices a lump in the neck; has a sore throat or difficulty in swallowing and may even struggle to breathe when lying down. The carcinoma is three times more common in females and males and especially in women aged 60 years and older.


While a doctor may feel that there is a lump or notice it during a physical exam, often a pathologist has to make the definitive diagnosis. This is because a carcinoma can only be diagnosed by looking at the type of cells in the nodule and particularly if the cells have invaded the capsule region. The actual carcinoma can vary from minimally invasive to very invasive, and all cases can result in death.


The Pax8-PPARγ fusion gene has been found to be expressed most often in patients with the carcinoma, and less often in those with adenoma, suggestive of this genetic factor as a potential cause of thyroid cancer. The RAt Sarcoma (RAS) gene mutations are also very often present with carcinoma suggesting another genetic cause. Such a gene is not found to be expressed in patients with adenoma.  Besides genetic factors, women seem to be more likely to get thyroid cancer, and carcinoma is more common in those women under 40 years of age. Having a goiter or being exposed to radiation are also potential causes of thyroid carcinoma. There is also some evidence that hyperthyroidism can be associated with higher risk of carcinoma or can make the condition worse.


Multiple approaches are often needed to treat carcinoma including therapy using radioactive iodine as well as surgery to remove most of the carcinoma.

Difference between Follicular adenoma and Carcinoma?


A follicular adenoma is a tumor of the thyroid that is benign and is completely surrounded by the capsule. A carcinoma is a tumor of the thyroid gland that is malignant and invades the capsule.

Benign or malignant

A follicular adenoma is always benign while a carcinoma is always a malignant tumor.


Follicular adenoma is much more common than carcinoma, being five times more prevalent, and adenoma is found in women mainly who are younger than 40 years of age. Carcinoma is rare and is most commonly found in women who are over 6o years of age.

Vascular penetration

Penetration of cells into the blood vessels never occurs with follicular adenoma. Penetration into blood vessels often is something that happens with carcinoma.


Treatment of follicular adenoma entails surgical removal of the tumor. Treatment of carcinoma often requires both surgical removal of a cancerous nodule and additional treatment such as with radioactive iodine. 

Table comparing Follicular adenoma and Carcinoma 

Summary of Follicular adenoma Vs. Carcinoma 

  • Both follicular adenoma and thyroid carcinoma cause nodules to develop in the thyroid gland.
  • The follicular adenoma is a benign condition in which the aberrant cells do not penetrate into or through the capsule area.
  • The carcinoma is a malignant cancer that can spread beyond the capsule and enter the blood supply.
  • Treatment for both conditions is surgery but for carcinoma additional options such as radioactive iodine therapy are also often needed and used.

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References :

[0]Hibi, Yatsuka, et al. "Is thyroid follicular cancer in Japanese caused by a specific t (2; 3)(q13; p25) translocation generating Pax8-PPARγ fusion mRNA?." Endocrine journal 51.3 (2004): 361-366.

[1]Hibi, Yatsuka, et al. "Is thyroid follicular cancer in Japanese caused by a specific t (2; 3)(q13; p25) translocation generating Pax8-PPARγ fusion mRNA?." Endocrine journal 51.3 (2004): 361-366.

[2]McHenry, Christopher R., and Roy Phitayakorn. "Follicular adenoma and carcinoma of the thyroid gland." The Oncologist 16.5 (2011): 585.

[3]Sherma, Steven I. "Thyroid carcinoma." The Lancet 361.9356 (2003): 501-511.

[4]Image credit: https://commons.wikimedia.org/wiki/File:Basal_cell_carcinoma_(2).jpg

[5]Image credit: https://commons.wikimedia.org/wiki/File:Follicular_adenoma_--_intermed_mag.jpg

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