Discuss the Risk Factors for Thyroid Cancer

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The Answer is The incidence of thyroid malignancies is significantly increased in populations exposed to excessive radioactive fallout in Japan following the atomic bombing in World War II and in Russia after the Chernobyl nuclear reactor accident. Longitudinal studies of populations exposed to radiation fallout indicate that diets deficient in iodine potentiate the risk of radiation-induced thyroid cancer and suggest that iodine supplementation has a protective effect against carcinogenesis.
A case control study conducted in Hawaii found that the risk of thyroid cancer increased with increasing body weight in both men and women. Men and women in the highest quartiles of weight had 5-fold and 2-fold increases in thyroid cancer risk, respectively, compared to those in the lowest quartiles. Additional investigations are needed in order to clarify the impact of radiation, iodine, body mass, female reproduction, and other risk factors on thyroid carcinogenesis in different populations.
Medullary thyroid cancer arises from the parafollicular calcitonin-secreting cells of the thyroid gland. While the majority of cases are sporadic (non-familial), approximately 25% involve heritable mutations of the RET gene, a proto-oncogene located on chromosome 10. The RET gene encodes a cell membrane receptor called receptor tyrosine kinase that activates signal transduction and complex cascades of biochemical reactions involving tyrosine phosphorylation within cells.
Mutations of the RET gene or the MENIN gene (a tumor suppressor gene located on chromosome 11) cause distinct heritable syndromes known as Multiple Endocrine Neoplasia (MEN). Endocrine tumors of the MEN syndromes elaborate a variety of amines and peptides depending upon the tissue of origin. Individuals who manifest MEN syndromes are classified into two major groups: MEN I (adenomas of the pituitary gland, islet cell tumors of the pancreas, hyperplasia of the parathyroid glands, and peptic ulcers) and MEN II (medullary thyroid carcinoma, pheochromocytoma, and occasionally mucocutaneous neuroma). These syndromes show an autosomal dominant inheritance pattern.
Carriers of certain mutated forms of the RET gene have a high lifetime risk of developing medullary thyroid carcinoma and pheochromocytoma (a malignant tumor of the adrenal glands). The familial association of medullary thyroid cancer and pheochromocytoma is called the Sipple Syndrome. Early onset, typically between 15 and 20 years of age, is a prominent characteristic of hereditary medullary thyroid cancer.

Discuss the Risk Factors for Thyroid Cancer

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