Thyroid neoplasm or thyroid cancer usually refers to any of four kinds of malignant tumors of the thyroid gland: papillary, follicular, medullary or anaplastic.
Thyroid cancer is the most common endocrine cancer. Estimated new cases and deaths from thyroid cancer in the United States in 2005:
- New cases: 25,690.
- Deaths: 1,490.
The incidence of thyroid nodules in the general population is 4%-7%, with nodules being more common in females than males. The prevalence of thyroid cancer in a solitary nodule or in multinodular thyroid glands is 10%-20%; the prevalence increases with irradiation of the neck in children and older men.
Between 1973 and 1997, the incidence of thyroid cancer increased by 24%, whereas mortality from this cancer decreased by 24%.
Women are affected more often than men (3:2 ratio).
Most patients are between the ages of 25 and 65 years at the time of diagnosis of thyroid carcinoma.
Race and ethnicity
Asian race has been shown to be a risk factor.
Japan and Hawaii have shown a higher incidence of thyroid cancers.
Causes and risk factors
Radiation fallout and radiotherapy given over the neck region in intermediate doses, frequently used between the 1940s and 1960s for the treatment of a variety of benign diseases (e.g. for acne, enlarged tonsils or thymus glands in children) increases the risk for thyroid cancer, particularly the papillary type. 4% of cases with thyroid cancer have a history of neck irradiation.
More recently it has been shown that patients treated with mantle-field irradiation for Hodgkin's disease are at increased risk of developing thyroid carcinoma, compared with the general population, although they are more likely to develop hypothyroidism than thyroid cancer.
The lag time between the onset of cancer and the radiation exposure averages between 20 to 30 years.
Medullary cancer of the thyroid may arise sporadically or as a dominant inherited syndrome of MEN type-II. Thyroid cancers including papillary and follicular carcinomas as well as breast neoplasms also occur frequently in Cowdwen's multiple hamartoma syndrome. Several oncogenes and tumor suppressor genes have been implicated in the pathogenesis of thyroid neoplasms.
Thyroid-stimulating hormone (TSH)
An increased risk for thyroid cancer may be present in patients with chronic TSH elevation such as patients with congenital defects in thyroid hormone formation.
Symptoms and signs
- Most thyroid cancers present as asymptomatic thyroid nodules which may be discovered incidentally in the course of radiological examination.
- An enlarging mass in the neck is the most frequent complaint. Patients may feel pressure symptoms from nodules as they begin to increase in size.
- Hoarseness of voice may result from recurrent laryngeal nerve paralysis. This also occurs with benign goiters.
- Neck pain or dysphagia.
On physical examination, a thyroid nodule that is hard or firm and fixed may represent a cancer. The presence of palpable enlarged nodes in the lateral neck, even in the absence of a palpable nodule in the thyroid gland, could represent metastases to the lymph nodes.
A variety of techniques are used to diagnose thyroid cancer. These include: thyroid isotope scans, ultrasonography and fine needle aspiration cytology (FNAC) or biopsy.
Thyroid isotope (nuclear) scans cannot differentiate absolutely a benign from a malignant nodule but can tell us about the probability of malignancy.
Hot thyroid nodules, which are able to concentrate radioiodine, represent functioning nodules and are less likely to be malignant. Cold nodules are nonfunctioning lesions that do not concentrate the isotope. Most thyroid cancers occur in cold nodules; however, only 10% of cold nodules are cancers.
Ultrasound imaging can detect nodules as small as 2 mm and is useful for determining the number of thyroid nodules and measuring their size.
A nodule in a gland with multiple other nodules of similar size is unlikely to be malignant. However, a dominant nodule in a multinodular gland carries a risk of malignancy similar to that of a true solitary nodule.
Ultrasonography can be used to determine whether a nodule is cystic or solid. Although most solid nodules are benign, thyroid carcinomas usually present as solid nodules. A cystic nodule or a mixed (cystic-solid) lesion is less likely to represent a carcinoma and more likely to be a degenerated colloid nodule.
Certain characteristics in a hypoechoic nodule increase the chance for malignancy. These include microcalcifications, central blood flow, or irregular border.
FNAC should be the initial diagnostic test for the evaluation of thyroid nodules. The accuracy of cytologic diagnosis from FNAC is 70%-80%.
Sensitivity of palpation increases with nodule size. The specificity of palpation in reaching a diagnosis ranges from 95 to 100%. In studies from referral centers, the reported sensitivity and specificity of FNA lies between 71-95 and 52-99%, respectively.
Ultrasound imaging can detect nodules as small as 2 mm and it is useful for determining the number of thyroid nodules and measuring their size.
Thyroid isotope scans
The thyroid concentrates iodine and so these scans are extremely sensitive in the detection of thyroid tissue. Thyroid isotope scans cannot differentiate absolutely a benign from a malignant nodule but can, based on the functional status of the nodule, assign a probability of malignancy.
FNA should be the initial diagnostic test for the evaluation of thyroid nodules. First, FNA can determine whether the lesion is cystic or solid. For solid lesions, cytology can yield one of three results: benign, malignant, or indeterminate. The accuracy of cytologic diagnosis from FNA is 70%-80%, depending on the experience of the person performing the aspiration and the pathologist interpreting the cytologic specimen.
Staging and prognostic factors
Thyroid cancer is cancer of the thyroid gland. These radioactive isotopes increase the chances of developing cancer, though thyroid cancer can develop even without any exposure to radioactivity.
Staging of thyroid cancer
- See staging system for thyroid cancer
Treatment of thyroid cancer
Although there are several types of thyroid cancer, the treatment is usually the same. The standard treatment includes surgery to remove the thyroid and any infected lymph nodes. People who have had their thyroid gland removed must take thyroid hormone in pill form to replace the hormone that was created by the thyroid. Surgery is generally followed by radioactive iodine therapy.
An alternative treament protocol based on newer research at the Mayo Clinic and USC Keck School of Medicine indicates that radioactive iodine treatments can and should be replaced by TSH (thyroid stimulating hormone) suppression therapy in low-risk patients.