Thyroid cancer occurs when malignant cells in the thyroid proliferate uncontrollably, forming tumors. Typically, thyroid cancer, in its most frequently-occurring forms, has an excellent prognosis with very high five-year survival rates and many patients are cured outright. Other forms of the disease may be highly aggressive and less responsive to therapy.
Thyroid cancer has many forms, and there are significant differences between them in terms of risk factors, diagnostic tests and treatment options.
The thyroid is a small, butterfly-shaped gland located at the base of the throat near the trachea that produces thyroid hormones made by follicular cells. Thyroid hormones regulate metabolism and calcitonin, which is made by parafollicular cells, or C-cells. Calcitonin regulates the body’s calcium levels.
Hypothyroidism refers to having too little thyroid hormone. If you are hypothyroid, your metabolism is slow, and you may experience weight gain, fatigue, depression, dry, itchy skin, dry, coarse and/or thinning hair, increased menstruation (heavier flow and/or more frequent periods), infertility and constipation. You feel generally sluggish, and may also feel cold frequently, particularly in the extremities.
Hyperthyroidism refers to an overactive thyroid, that is, one which produces too much thyroid hormone. The metabolism is abnormally fast and, as might be expected, the symptoms of hyperthyroidism are the polar opposite of hypothyroidism. They include: weight loss (despite a normal appetite), sweating, decreased menstruation, nervousness, insomnia, hand tremor, thinning skin, fine, thinning hair, rapid heartbeat and more frequent bowel movements or diarrhea.
When your thyroid hormone levels are normal, this is called euthyroid. Many patients diagnosed with thyroid cancer are euthyroid.
A thyroid nodule is a lump that develops in the thyroid. Depending on its size, it may be palpable or visible as a swelling in the neck. Most thyroid nodules are benign, but a small percentage are malignant.
The term “goiter” simply refers to an enlargement of the thyroid, which may be diffuse or nodular. Many goiters are multinodular as opposed to a solitary nodule. Goiters can occur in hyperthyroid, hypothyroid and euthyroid patients and generally develop as a result of increased TSH levels.
Types of Thyroid Cancer
Papillary thyroid cancer is the most common type of thyroid cancer, accounting for over 80 percent of cases. It is usually slow-growing, localized to the thyroid, well-differentiated and has an excellent prognosis with high survival rates.
Follicular thyroid cancer, as the name implies, originates from follicular cells. It is also usually slow-growing, localized to the thyroid. Follicular thyroid carcinoma has a good prognosis with high survival rates.
Hurthle cell carcinoma is a type of follicular carcinoma in which a specific kind of cell (the Hurthle cell) is predominant in the tumor. Hurthle cell cancers are slightly more aggressive than other follicular carcinomas. They are less likely to take up radioiodine, which is significant because radioiodine ablates (destroys) residual thyroid tissue, and is thus an important treatment modality. They are also more likely to have nodal metastases (spread to neighboring lymph nodes).
Anaplastic thyroid carcinoma is a type of follicular carcinoma that is thought to originate from well-differentiated papillary or follicular cancers through a process called dedifferentiation.
Medullary thyroid cancer develops in the C-cells of the thyroid. More than any other type of thyroid cancer, medullary thyroid cancer has a well-established genetic component, with a sizable proportion of cases thought to be an inherited form of the disease.
This cancer originates from lymphoid tissue in the thyroid (as opposed to carcinomas, described above, which develop from epithelial cells). It is very rare, and often develops in patients who have a history of chronic thyroiditis. It is often treated similarly to other forms of non-Hodgkin lymphoma.