Thyroid cancer is the most common malignancy of the endocrine system. These lesions result from the uncontrolled cellular growth, the abnormal cells may involve the adjacent tissues and spread to other body parts.
Thyroid cancer incidence is higher in women, although the prognosis is worse for men. The malignant neoplasms of the thyroid can arise from any cells which comprise the gland: follicular cells (which produce and store thyroid hormones), calcitonin-producing medullary C cells, lymphocytes, and stromal and vascular elements. The more differentiated are the cells which compose the tumor the better prognosis is, whereas anaplastic tumors are associated with a worse prognosis.
In general, it is considered that exposure to radiation increases the risk of developing benign or malignant neoplasms of the thyroid.
Differentiated thyroid cancer
Differentiated thyroid cancers are derived from the follicular cells of the thyroid gland. The incidence of differentiated thyroid carcinomas increases with age.
- Papillary carcinoma
Papillary cancer is detected in about 80% of all thyroid cancers with a higher incidence among women rather than men. Typically, these tumors occur in individuals between 30 and 50 years of age with a higher incidence in women. The tumor is firm, has no capsule or is partially encapsulated. The primary lesion may be very small, less than 10 mm in diameter, it grows slowly and for many years may remain confined to the thyroid. Sometimes these tumors metastasize to lungs or bones.
- Follicular carcinoma
This type of cancer rarely spreads to cervical lymph nodes. Sometimes follicular carcinoma cells secrete thyroid hormones and may cause hyperthyroidism. Metastases are usually found in bones, lungs, and brain.
Anaplastic carcinomas constitute 1-2% of all thyroid carcinomas and are typically detected in older patients with a median age of 65 with rapid enlargement of the thyroid over several months. This type of carcinoma is highly malignant and the adjacent organs are involved quickly.
Primary thyroid lymphomas are rarely seen, although more common in older women who have a history of autoimmune thyroid disease.
Medullary carcinoma arises from the C cells of the thyroid that produce calcitonin. Hypercalcitoninemia (high blood levels of calcitonin) is associated with severe, watery diarrhea. These lesions comprise almost 10% of all thyroid cancers. In 70-90% of case, medullary carcinoma occurs spontaneously, whereas in 10-30% there is a genetic predisposition and medullary carcinoma occurs as one of the features of the MEN syndrome – multiple endocrine neoplasia characterized by the various tumors of endocrine glands.
All of the thyroid tumors usually are asymptomatic. However, the advanced disease may present with:
- local neck discomfort, sometimes painful neck mass;
- hoarse voice;
- difficulties swallowing;
- difficulties breathing due to the tracheal compression.
An ultrasound examination is performed to identify and estimate the size and spread of the lesion. Increased calcitonin levels are suggestive of medullary thyroid cancer. Fine needle aspiration biopsy is necessary to make the diagnosis.
Radioactive iodine scanning of the thyroid and the whole body may be used after the thyroidectomy to check for the remaining cancerous tissues. CT, MRI and PET scanning are typically performed to identify possible metastases of the primary tumor.
Usually, the tumor should be removed surgically followed by chemotherapy.
- Surgical management
Thyroid cancer requires the removal of the whole thyroid – total thyroidectomy should be performed. Partial removal of the thyroid is also possible (lobectomy, hemithyroidectomy). Local lymph nodes should also be removed. Removal of the thyroid should be followed by replacement therapy with levothyroxine.
- TSH suppression therapy
The thyroidectomy should be followed by the thyroxine replacement to suppress TSH.
- Radioiodine therapy
Radioactive iodine is administered after thyroidectomy in order to destroy the remaining cancerous tissues and healthy thyroid. Recurrent thyroid cancer may also be treated with radioactive iodine.
- External radiotherapy
External beam radiation may be used in the treatment of bone metastases or in case of anaplastic thyroid carcinoma.
Zoledronate is administered in case of bone metastases. Thyroid cancer metastases are refractory to radioiodine therapy may be treated with vandetanib, sunitinib or lenvatinib.