Radiation exposure, either therapeutic such as for the treatment of Hodgkin’s disease or environmental (e.g., Chernobyl disaster), increases the risk of thyroid cancer. Family history of thyroid cancer in a first-degree relative or history of familial syndromes such as MEN-2 and Li-Fraumeni syndrome is an intrinsic risk factor.

World Health Organization (WHO) and Armed Forces Institute of Pathology (AFIP) classified thyroid cancer into three main categories (Table 8.2). Epithelial tumors constitute of more than 95 % of cases with majority being papillary thyroid carcinomas.

Most commonly encountered distant metastasis sites include lungs, brain, bones, and liver. The vertebrae, pelvis, ribs, long bones (e.g., femur), and skull are the skeletal sites commonly involved. About 2–10 % of patients with papillary thyroid cancer and 15–20 % of patients with follicular cancers have distant metastases. Two-thirds of these patients have pulmonary and one-fourth has skeletal metastases. Bony metastasis occurs more frequently in subjects with follicular cancer due to hematogenous dissemination [3].

Follicular thyroid tumors can have a higher prevalence of distant metastasis than papillary thyroid cancers. The risk of distant metastasis is higher when the primary tumor size is >20 mm [4]. However, even smaller tumors have been reported to cause distant metastasis. Morbidity and mortality increase in patients with distant metastasis. Prognosis in distant metastasis depends upon the histology of the primary tumor, the number of metastasis, the age at diagnosis, and the avidity of radioactive iodine (RAI) . The overall 10-year survival rate is 40 % when distant or skeletal metastases are present. In addition, age >45 years at the time of diagnosis and symptomatic metastasis are associated with worse prognosis [5, 6].