Cancer of the thyroid is the most common endocrine malignancy, although it is an uncommon cancer, comprising only about 1 percent of invasive cancers.
Although invasive thyroid cancer is uncommon, doctors often have to diagnose and treat thyroid nodules, since about 4 percent of adults develop them.
Thyroid cancer commonly appears as a "cold" nodule, meaning that it does not take up radioactive iodine. About 20 percent of cold nodules are cancer.
About 90 percent of thyroid cancers develop from the follicular cells. Some develop from the parafollicular cells or C cells (medullary).
Patients with well-differentiated tumors generally have a good prognosis. Those with undifferentiated or anaplastic tumors do not.
Papillary carcinomas are generally slow-growing, with an 80 percent overall survival at 10 years. Even when tumors spread to regional lymph nodes or the lungs, survival may be more than 10 years.
Tiny, clinically insignificant papillary carcinomas are found in 5 to 10 percent of thyroid glands examined at routine autopsies.
Follicular carcinomas occur in patients about 10 years older than those who get papillary carcinomas. Although these tumors are also usually slow growing, they behave somewhat more aggressively than papillary carcinomas and are more likely to spread to the lungs or bones.
Three percent of thyroid cancers are undifferentiated (anaplastic) carcinomas. They occur in older patients, grow rapidly, behave aggressively and respond poorly to treatment.
Medullary carcinomas make up almost 5 percent of thyroid cancers. These tumors secrete calcitonin, a tumor marker that is helpful in diagnosis and follow-up and also in screening relatives of those affected, since this tumor may occur on a familial, or inherited, basis.
Papillary carcinomas spread to nearby lymph nodes and the tissues in the neck, with metastatic lesions to the lungs and bones. These tumors spread through the bloodstream with metastasis occurring more often to bone.
Anaplastic carcinoma usually extensively invades surrounding tissue. Medullary carcinoma spreads to lymph nodes and may invade blood vessels with metastases to the liver.
A number of factors affect the prognosis for papillary and follicular thyroid cancers. A better prognosis can be expected with a pure papillary carcinoma in younger patients (women under 50 and men under 40), a tumor smaller than 3/4 inch (2 cm.) small diffuse metastases, female sex, and low-grade lesions.
A worse prognosis is related to age over 40, the degree of invasion (vascular and thyroid capsule) in follicular carcinoma, distant metastases, a large tumor (especially over 1 1/2 inch (5cm), large nodular metastases, male sex and high-grade lesions (aneuploid).
Most cases occur between 25 and 65 years of age, and the age at diagnosis is one of the most important factors in predicting prognosis. Men under 40 and women under 50 have significantly lower rates of recurrence and better survival rates than older persons.
Some thyroid cancers tend to run in families, but most often the cause is unknown and there is no genetic link.
In early thyroid cancer, there are typically no symptoms. It is often discovered on a routine exam as a nodule in the thyroid gland (in the front of the neck just below the Adam's apple).
In advanced stages, symptoms and signs relate to the type of cancer and whether it has metastasized.
Diagnosis is based upon clinical history, findings on examination, scanning tests and blood tests. Additionally, biopsy material may be taken to establish the definitive diagnosis.
The primary treatment of thyroid cancer is surgery, but there are some differences in opinion about the extent of thyroid resection required for the best prognosis.
A near-total thyroidectomy - removing almost all of the thyroid - offers the best chance of cure, especially if the cancer is in several places within the gland. The removal of all functioning thyroid tissue also makes it possible to scan for metastatic disease with radioactive iodine and to use serum thyroglobulin values to detect persistent disease.
One of the risks of total thyroidectomy is the inadvertent removal of the parathyroid glands, which are situated, two on each side, at the edge of the thyroid. When a total thyroidectomy is done, an attempt is usually made to leave all four parathyroid glands in place.