Overview of Thyroid Cancer

Cancer is something that all doctors keep in the back of their minds as a worst case scenario. Therefore, it should always be in the differential so it can be ruled out. In any patient that presents with a neck mass, swollen lymph nodes, enlarged thyroid gland, or thyroid nodule, thyroid cancer must be ruled out. Below is an overview of the five main types of thyroid cancer.

Of all cancers involving the endocrine system, thyroid cancer is the most frequently encountered. Risk factors include advanced age, female sex (2:1), increased thyroid nodule size (≥ 4 cm), metastases, local tumor spread, and a history of head or neck radiation exposure during childhood. Factors for a worse prognosis include male sex and age < 20 or > 45.

Thyroid cancers are classified into five main types listed below:

1. Papillary
2. Follicular
3. Medullary
4. Undifferentiated (Anaplastic)
5. Lymphoma

Papillary thyroid cancer is the most common. It has several distinguishing pathologic features which include orphan-Annie (or ground-glass) nuclei (nuclei that look blank), psammoma bodies (cells filled with calcium), and development of papillae. It usually spreads through the lymph system, with metastasis to the lungs, bones, and cervical lymph nodes. It can be diagnosed easily in the early stages by fine needle aspiration, and has an excellent survival rate. 
  
Follicular thyroid cancer presents most commonly as a solitary thyroid nodule. Risk factors include female sex and residence in an area with low dietary iodine. Factors for a worse prognosis include age > 50, presence of Hurthle cells, tumor size > 4 cm, remote metastases, and blood vessel involvement. Its distinguishing pathologic features include follicles with a similar appearance, and blood vessel involvement. It usually spreads through the blood, with metastasis to the lung, bones, and CNS. It is harder to diagnose by fine needle aspiration, but still has a good survival rate.

The treatment of papillary and follicular thyroid cancers is the same. The treatment of choice is surgical removal of most or all of the thyroid gland, along with removal of any involved lymph nodes. Treatment with radioactive iodine (¹³¹I) is performed several weeks later to kill any remaining thyroid cells. Levothyroxine is also used to suppress TSH to help prevent the tumor from growing.

Medullary thyroid cancer presents most commonly as sporadic, but can also run in families. The familial form is associated with MEN II and MEN III. The sporadic form is associated with a worse prognosis. Its distinguishing pathologic features include the making of calcitonin (because it originates from the parafollicular C cells) and the presence of amyloid. It is able to be diagnosed by fine needle aspiration and measuring calcitonin levels. The treatment of choice is surgical removal of the entire thyroid gland. It is not responsive to radioactive iodine. Patients can be screened for the RET mutation in instances of the familial form, with surgical removal of the thyroid gland if positive.

Undifferentiated (Anaplastic) thyroid cancer presents most commonly in older females. Risk factors include follicular thyroid cancer in the past or presence of a multinodular goiter. It is very aggressive and has a very low survival rate including death usually within six months. The treatment of choice, if effective, is radioactive iodine. Chemotherapy typically does not work. Surgery can be performed for palliative reasons, usually for mass effect on the airways.

Lymphoma of the thyroid gland presents most commonly from Hashimoto’s thyroiditis, and is usually diffuse large B-cell lymphoma. Risk factors include a fast growing mass in the thyroid. The treatment of choice is radiation therapy.

In conclusion, it is important to rule out thyroid cancer in any suspicious presentation. As you can see above, some types are very treatable with a good prognosis, while others are not. With any cancer, it is imperative to make the diagnosis early and to completely explain the risks, benefits, alternatives, and treatment options to every patient.

Sources:

Fauci, Anthony S., and Tinsley Randolph Harrison. "Disorders of the Thyroid Gland." Harrison's Principles of Internal Medicine. 17th ed. New York: McGraw-Hill Medical, 2008. Print.

Le, Tao, and Vikas Bhushan. "Endocrine." First Aid for the USMLE Step 1. 2010 ed. New York: McGraw-Hill Medical, 2010. 293. Print.

Goljan, Edward F. "Endocrine Disorders." Rapid Review Pathology. 3rd ed. Philadelphia, PA: Mosby/Elsevier, 2010. 490-91. Print.