1) Thyroid cancer risk factors include a history of radiation exposure to the thyroid gland, family history of thyroid cancer, and certain genetic syndromes. The risk increases linearly with radiation dose up to 2000 cGy. 2) The RET proto-oncogene plays a significant role in thyroid cancers, including medullary thyroid carcinoma (MTC). Germline RET mutations predispose to MEN2 syndromes and familial MTC, while somatic mutations occur in 30% of MTCs. 3) RET gene fusions also function as oncogenes in papillary thyroid carcinoma (PTC), especially in young patients and after radiation exposure. RET/PTC signaling involves the MAPK pathway