Thyroid cancer refers to formation of malignant cells in the thyroid gland. Accumulation of these cells forms a cancerous growth in the thyroid which often takes the form of a nodule (thyroid nodule) at the beginning.
There are various types of thyroid cancer, named depending on group of cells affected:
- Papillarythyroid cancer – papillary thyroid cancer is the most common type of thyroid cancer; it affects mostly women aged between 30 and 40. Usually, papillary thyroid cancer grows slowly, and tends to have good prognosis when diagnosed early. The tumor develops in the cells that produce the triiodothyronine, one of the thyroid hormones.
- Follicular Thyroid Cancer– this type of thyroid cancer, although a little slow growing, tends to grow quicker than papillary carcinoma. It occurs mostly in women, principally women over 50 years old. Prognosis of follicular cancers is not alarming when diagnosed and treated early. Usually, follicular thyroid cancers develop in the cells of the thyroid gland that produce and secrete thyroxine (thyroid epithelial cells, also called follicular cells or principal cells).
- Medullary Thyroid Cancer – this form of thyroid cancer is more aggressive than papillary and follicular cancers; it has poor prognosis. It tends to spread to distant organs in the body: liver, bone, brain, and adrenal medulla. Medullary cancer usually begins in the parafollicular cells(or C cells). This group of thyroid cells produces and secretes calcitonin, an hormone that acts by keeping the blood calcium at normal levels. About 25 percent of medullary thyroid cancer is due to genetic disorders.
- Anaplastic thyroid cancer – unlike papillary carcinoma and follicular thyroid cancer, anaplastic thyroid cancer is a very life-threatening condition; it tends to grow rapidly, and resist to treatments. Due to its metastatic characteristic, anaplastic thyroid cancer has a very poor prognosis. Usually, the tumor begins in the follicular cells of the thyroid, and affects most often people aged 60 and over. Anaplastic thyroid cancer is rare, representing about 3% of all thyroid cancers.
- Thyroid lymphoma – this is a very rare form of thyroid cancer. Usually, the cancer begins in the immune system cells of the thyroid (lymphoma cells). Development of thyroid lymphomais often associated with preexisting chronic autoimmune disease of the thyroid gland called thyroiditis (inflammation of the thyroid gland).