While the great majority of thyroid nodules are benign, approximately 5% of thyroid nodules harbor cancer. Relative to other cancers, thyroid cancers are rare, accounting for approximately 1.5% of cancers in adults and 3% in children. There are several different types of thyroid cancer, which can be divided into two groups, well-differentiated and not well-differentiated. The well-differentiated cancers are derived from the predominant cell type in the thyroid gland, the follicular epithelial cell. They comprise 90% of thyroid malignancies. This group includes papillary thyroid cancer and follicular cell carcinoma.
Papillary cell carcinoma is by far the most common type of thyroid cancer, accounting for approximately 85% of well-differentiated thyroid carcinomas. It is more common in young females, and usually presents as an asymptomatic, slow-growing, palpable nodule in the neck. As with all tumors, when the nodule gets larger, it my cause symptoms of hoarseness, problems swallowing, or shortness of breath. 15-30% of patients with papillary thyroid carcinoma may present with metastases in the lymph nodes within the neck.
In papillary thyroid carcinoma, the normal organization of the thyroid gland is taken over by “papillae”, which include cancerous cells. Calcifications, or calcium deposits, within the cells are characteristic of this type of carcinoma.
The treatment of papillary thyroid carcinoma typically involves removal of the entire thyroid gland, which is called a total thyroidectomy. Occasionally, small papillary cancers <1.0 cm. may be treated with removal of only half of the thyroid gland, termed a thyroid lobectomy or hemithyroidectomy. If there are clinically evident lymph nodes in the neck, a neck dissection is also indicated. The 5-year survival for papillary thyroid carcinoma is >95%, and 20 year survival for early stage favorable thyroid cancer is roughly equivalent to that of the general population.
Follicular cell carcinoma is the second most common type of thyroid cancer, accounting for approximately 10-13% of well-differentiated thyroid cancers. It is more common in the elderly and in females, and usually presents as a slow-growing, painless neck nodule. 20-50% of this type of carcinoma may have distant metastases, typically to the lung or bone.
As with all thyroid nodules, the workup for a follicular carcinoma involves a blood TSH level, an ultrasound, and a fine needle aspiration (FNA). When an FNA reveals follicular neoplasm, thyroid lobectomy is required to determine whether the nodule is a benign adenoma or a follicular cell carcinoma.
The treatment for follicular cell carcinoma involves either a thyroid lobectomy or a total thyroidectomy, depending on the size and involvement of the tumor. The overall 5-year survival for follicular cell carcinoma is 70-85%. Spread of the carcinoma beyond the thyroid capsule and invasion of blood vessels are associated with more aggressive tumors.
Hürthle Cell Carcinomas are a rare subtype of well-differentiated thyroid carcinoma, accounting for approximately 3% of thyroid carcinomas. They are more aggressive and more likely to metastasize than other types of well-differentiated thyroid carcinoma. Like follicular cell carcinoma, the diagnosis of a Hürthle cell carcinoma requires an open biopsy because on FNA, Hürthle cell tumors can be benign Hürthle cell adenomas or Hürthle Cell carcinoma.
If a Hurthle cell carcinoma is found on open biopsy, the treatment for Hürthle cell carcinoma is a total thyroidectomy followed by radioactive iodine treatment. However, Hürthle cell carcinomas are less sensitive to radioactive iodine therapy than other types of well-differentiated carcinoma.
Medullary thyroid carcinomas are derived from one of the non-predominant cell types within the thyroid gland, the parafollicular C cells, and account for 4-9% of thyroid cancers. It is the third most common type of thyroid cancer, behind papillary and follicular carcinoma. There are two types of medullary thyroid carcinoma, a familial type, accounting for 20-25% of medullary cancers, and a sporadic type, accounting for the remaining 75-80%. The familial type is typically related to a syndrome called “Multiple Endocrine Neoplasia”, which involves a history within first-degree relatives of other endocrine malignancies, including pheochromocytoma and either
parathyroid hyperplasia or mucosal neuromas. This syndrome is caused by an inherited mutation in the RET proto-oncogene. Medullary thyroid carcinoma typically presents with multiple, bilateral nodules in the familial type, whereas it is usually in a single nodule and unilateral in the sporadic type.
Because the parafollicular C cells produce a hormone called Calcitonin, the workup for medullary thyroid carcinoma involves checking a serum Calcitonin level. Because of the possible familial type, patients with medullary thyroid carcinoma should be screened for a family history of Multiple Endocrine Neoplasia, and genetic testing to determine the mutation and presence of mutations in family members is available.
The treatment for medullary thyroid carcinoma involves a total thyroidectomy. This tumor often spreads to lymph nodes, and dissection of lymph nodes in the neck is generally performed.
Patients are followed with frequent monitoring of serum Calcitonin levels to detect recurrence.
Anaplastic carcinoma is a very aggressive subtype of thyroid cancer, accounting for <2% of all thyroid cancers. It is more common in the elderly, and typically presents with a very fast-growing firm thyroid mass. It often presents with hoarseness, representing local invasion affecting the vocal cords.
Unfortunately, anaplastic carcinoma often presents with metastatic disease, and has an overall 5-year survival of less than 10%. Surgical management generally consists of performing a tracheostomy to secure the airway. Occasionally the tumor may be discovered in early stages as early transformation of papillary thyroid cancer into anaplastic carcinoma. In these cases, aggressive surgery is performed. External beam radiotherapy may be performed to slow growth of the tumor, and there are new chemotherapeutic agents that have shown encouraging results in this very aggressive tumor. The most common site of distant metastasis is the lungs, with the
bone and brain also being fairly common.
Primary lymphoma of the thyroid gland accounts for less than five percent of all thyroid cancers, and is typically of the non-Hodgkin’s type. Usually, this type of lymphoma arises from lymph nodes, but the thyroid gland is one of the non-nodal sites that this can arise from, accounting for approximately 3% of non-Hodgkin’s lymphomas. There is a known association between primary lymphoma of the thyroid and Hashimoto thyroiditis, an autoimmune disorder that can lead to hypothyroidism. However, Hashimoto’s thyroiditis is very common, and the vast majority of patients with Hashimoto’s thyroiditis will never develop lymphoma.
Primary lymphoma of the thyroid typically presents as a rapidly-growing thyroid mass and can cause symptoms of hoarseness, difficulty swallowing, and cough or shortness of breath. The workup includes a biopsy to confirm the diagnosis, and a systemic evaluation to determine the extent of systemic spread of disease. Complete blood count, bone marrow evaluation CT scanning, and PET scanning are generally performed, as determined by the treating medical oncologist. Fine needle aspirate can make the diagnosis, but often an open biopsy is required to confirm the diagnosis and provide specific classification of the lymphoma.
The treatment of primary lymphoma of the thyroid follows the treatment of lymphoma in other sites, and includes a combination of chemotherapy and external beam radiation. It is a highly curable disease process if diagnosed and treated early.