| Thyroid cancer is a tumor that develops in the tissue of the thyroid gland, which is located at the base of the neck and regulates body's metabolism. Most thyroid cancers present as a small mass of regular or irregular shape (nodule). There may be either single or multiple nodules. Although 90% to 95% of nodules and tumors of the thyroid are benign ("Detailed Guide"), there are four main types of thyroid cancer: papillary, follicular, medullary, and anaplastic thyroid carcinomas. Papillary and follicular carcinomas (together referred to as differentiated thyroid cancer, or DTC) comprise 80% to 90% of all thyroid cancers ("Detailed Guide").
Papillary carcinoma, also called papillary cancer or papillary adenocarcinoma, develops from thyroid follicle cells. Eighty to ninety percent of the time, these tumors develop only in one lobe of the thyroid ("Detailed Guide"). Tumors vary in size from microscopic to several centimeters in diameter. These are slow-growing cancers that may spread (metastasize) to lymph nodes.
Follicular carcinoma, also called follicular cancer, is the second most common type of thyroid cancer. This cancer may occur in any part of the thyroid and in a wide variety of sizes. These tumors are well defined when small, but as they enlarge, they may invade both the blood vessels and outer covering (capsule) of the thyroid. Follicular cancer is less likely to metastasize than papillary cancer but may spread via the bloodstream to the bones, lungs, liver, and brain.
Medullary carcinoma accounts for about 5% of all thyroid carcinomas ("Detailed Guide"). The growth rate of medullary carcinomas varies widely. There appear to be two types of medullary cancer. Sporadic medullary carcinoma develops mainly in older adults and is not inherited. Familial medullary thyroid cancer appears to be inherited. It accounts for up to 20% of cases of this type of thyroid cancer ("Detailed Guide").
Anaplastic carcinoma, also called undifferentiated thyroid cancer, is an uncommon, aggressive type of thyroid cancer that accounts for 1% to 2% of thyroid carcinoma (Sharma). Anaplastic carcinoma is thought to develop from papillary or follicular cancer cells. This type of thyroid cancer is very invasive, spreading rapidly to the neck and other parts of the body.
A general summary of the staging of thyroid cancer is as follows:
Papillary and follicular cancer for individuals under age 45: stage I, cancer has not spread to distant sites; stage II, cancer has spread to distant sites.
Papillary and follicular cancer for individuals over age 45 and medullary thyroid cancer for all ages: stage I, tumors less than 2 cm. Cancer has not spread to local lymph nodes or distant sites. Stage II, tumors are 2 to 4 cm. Cancer has not spread to local lymph nodes or distant sites. Stage III, tumors are larger than 4 cm. Cancer has grown outside thyroid gland but has not spread farther than local neck nodes. Stage IV, cancer has spread to distant sites or grown into neck, spine, or large blood vessels.
All anaplastic cancers are considered stage IV, because they are so rapidly invasive.Risk: Age is the most predictive risk factor for individuals developing thyroid cancer. Most thyroid cancer is diagnosed in individuals between the ages of 30 and 50 ("Detailed Guide"). The likelihood of recurrence is increased if the first diagnosis is made before age 20 or after age 60; 3 times as many new cases are diagnosed in women as in men (Sharma). Other factors that may increase the risk of developing thyroid cancer are a diet low in iodine and exposure to radiation during childhood and adolescence. Some types of medullary thyroid carcinomas appear to run in families as the result of inheriting an abnormal gene. Incidence and Prevalence: Thyroid cancer constitutes about 1% of all malignant tumors. In the US, the American Cancer Society estimates that about 23,600 individuals will be diagnosed with thyroid cancer in 2004. Annually, 1,460 people die from the disease ("Detailed Guide"). Although international incidence statistics are not available, thyroid cancer is more prevalent in landlocked, underdeveloped countries where there is little iodine in the diet. |
Source: Medical Disability Advisor