Different Types of Thyroid Cancer
About Thyroid Cancer
The thyroid is a small endocrine (hormone-producing) gland located at the front of the neck. The hormones produced by the thyroid are involved in the control of body metabolism and temperature.
There are several types of thyroid cancer, which can vary in cause, symptoms, and severity. The most common are follicular adenocarcinoma and papillary adenocarcinoma of the thyroid.
Thyroid cancer risk factors include age, sex, family history, iodine deficiency, and radiation exposure. People over forty, women, and people with a family history of thyroid cancer all have an increased risk. Iodine deficiency can slightly increase the risk of some types of thyroid cancer, and previous radiation exposure, especially to the neck, is a very strong risk factor for all types.
Common Thyroid Cancer Types
Two varieties of thyroid cancer, papillary and follicular cancer, account for nine out of ten cases of thyroid cancer. Both types develop in the hormone-producing cells of the thyroid gland.
Papillary Adenocarcinoma
This type of thyroid cancer comprises approximately 80% of cases. This is a slow-growing thyroid cancer and is consequently easy to treat successfully. Despite this, there is a still a danger of the cancer spreading to the lymph nodes of the neck, which can lead to metastasis (spread to other body tissues).
This cancer most commonly develops in people in their thirties and forties. Women are three times more likely to develop this cancer than men. Papillary adenocarcinoma can occur in conjunction with hereditary diseases such as Gardner syndrome, or non-hereditary diseases such as Hashimoto’s thyroiditis.
Papillary thyroid cancer most often spreads to the neck, and in 5 to 10% of people, to more distant locations such as the lungs and bone.
Follicular Adenocarcinoma
This thyroid cancer is the second most common of the various types. Approximately 10% of people with thyroid cancer have follicular adenocarcinoma. As with papillary adenocarcinoma, the follicular variety is three times more common in women than in men; however follicular thyroid cancer is more common in people aged in the forties and fifties.
In countries or regions where iodine deficiency is common, the incidence rate of this type of cancer is slightly elevated.
It is less common for follicular adenocarcinoma to spread to the lymph nodes of the neck, but metastases to lungs, bone, and other distant locations is more common, with a frequency of approximately 20%.
Treatment
Papillary and follicular thyroid cancers are generally treated in the same way. Early-stage cancers are treated with surgery to remove part or all of the thyroid gland. This surgery is followed up with an additional treatment such as radiation therapy or hormone therapy, to ensure any remaining cancer cells are killed.
Later stage cancers are more likely to be treated with total thyroid removal rather than partial removal. Additional treatments might include further surgery to remove cancer from sites of metastases, and chemotherapy or experimental treatment.
Both types respond well to radiation therapy with radioactive iodine. This is because both types develop in the hormone-producing cells of the thyroid. These cells are the only cells in the body that absorb iodine, and as such respond to treatment with radioactive idoine, which kills the cancer cells while leaving other cell types in the body largely unharmed.
Uncommon Types of Thyroid Cancer
The remaining types of thyroid cancer, which include thyroid lymphoma, thyroid sarcoma, medullary thyroid cancer, and anaplastic thyroid cancer, account for approximately 10% of all cases.
These cancers do not respond to radiation therapy with radioactive iodine, as they do not develop in the iodine-absorbing cells of the thyroid.
Medullary Thyroid Carcinoma
This thyroid cancer develops in cells called C cells, and makes up around 5% of all thyroid cancer cases. C cells produce a hormone called calcitonin, which is involved in calcium regulation. Some medullary thyroid cancers are sporadic, meaning they occur in the absence of a family history of the cancer. Approximately 20% of cases of medullary cancer are familial, meaning they are inherited. These cancers often develop early, and can appear in young adults or even children.
Medullary thyroid cancer treatment commonly consists of thyroid-removal surgery, and chemotherapy or external-beam radiation therapy. If metastases exist these must also be surgically removed.
Anaplastic Thyroid Cancer
This type of cancer is responsible for just 2% of all thyroid cancers. This cancer is very hard to treat, because it spreads easily and aggressively to other parts of the body. The rarity of this cancer type means little is known about cause and prevention, and adds to the difficulty of determining an effective treatment.
Treatment for anaplastic thyroid cancer includes chemotherapy or external beam radiation therapy. Surgery to remove the thyroid gland is sometimes not an aggressive enough treatment – in these cases, a tracheostomy is often necessary.
Thyroid Lymphoma
A lymphoma is a type of cancer that develops from lymphocytes, a type of immune cell. Lymphomas usually develop in lymph nodes, but can occasionally develop in the thyroid, as this gland is a site of immune system activity.
When diagnosed correctly and early, this type of thyroid cancer can be treated completely. Treatment is generally a combination of surgery, chemotherapy, and radiation therapy, depending on the requirements of the patient and the extent of the cancer’s advancement.
Thyroid Sarcoma
Thyroid sarcoma develops in structural thyroid cells. This is an aggressive and treatment-resistant cancer type. Thyroid sarcoma is much more difficult to treat, and has a worse prognosis, than the other varieties. Treatment might include a combination of surgery, radiation therapy, or chemotherapy.
References
American Cancer Society: What is Thyroid Cancer?
Memorial Sloan-Kettering Cancer Center: Risk Factors
Memorial Sloan-Kettering Cancer Center: Thyroid Cancer Overview
National Institute of Health MedlinePlus: Thyroid Cancer
U.S. National Cancer Institute: Thyroid Cancer Treatment
