Contributor: Gordon K. Klintworth 
Several different types of  carcinoma arise in the thyroid gland. They  include: papillary carcinoma [carcinoma - papillary], follicular cell carcinoma [carcinoma - follicular cell], squamous cell carcinoma [carcinoma - squamous cell], medullary carcinoma [carcinoma - medullary], mucoepidermoid carcinoma anaplastic carcinoma [carcinoma - anaplastic thyroid] and Hürtle cell carcinoma [carcinoma - Hürtle cell]. Risk factors include ionizing radiation (especially to individuals <20 years old), and mutations in the RET gene. Carcinomas of the thyroid gland can spread by the lymphatic vessels to the regional lymph nodes. Distant metastases can reach distant sites including the uvea and orbit [carcinoma - metastatic]. The most common type of thyroid carcinoma  is a papillary carcinoma [carcinoma - papillary thyroid], which typically invades the lymphatic vessels and spreads to regional lymph nodes. It accounts for ~70% of thyroid carcinoma. Medullary carcinoma of the thyroid gland [carcinoma - thyroid medullary] is assocaited with multiple endocrine neoplasia syndrome. The follicular carcinoma spreads mainly by the blood stream to distant organs, such as the lungs and bone. The other primary malignant neoplasms of the thyroid gland are rare. Squamous cell carcinoma of the thyroid gland is very rare and is usually found in older patients with a history of goiter.