Thyroid cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up.

Thyroid cancer is the most common of the endocrine malignancies and it represents <1% of all human tumors. The annual incidence of thyroid cancer varies considerably by geographic area, age and sex. A recent review reported an overall incidence of all types of thyroid cancer in the USA of 7.7 per 100 000 person-years, with rates of 11.3 per 100 000 woman-years and 4.1 per 100 000 man-years [1]. The incidence of papillary thyroid cancer is 5.7 per 100 000 person-years, with rates of 8.8 per 100 000 woman-years and 2.7 per 100 000 man-years [1]. Among women, papillary thyroid cancer incidence rates are higher among Asians (10.96 per 100 000 woman-years) and lower among blacks (4.9 per 100 000 woman-years). Among men, papillary thyroid cancer incidence rates are higher among whites (3.58 per 100 000 woman-years) and lower among blacks (1.56 per 100 000 woman-years) [1]. The incidence of follicular thyroid cancer in the USA is 0.82 per 100 000 person-years, with rates of 1.06 per 100 000 woman-years and 0.59 per 100 000 man-years. The incidence of follicular cancer does not vary substantially by race/ethnicity [1]. The incidence rates of medullary thyroid cancer (MTC) and anaplastic thyroid cancer (ATC) are 0.11 and 0.21 per 100 000 personyears with no noted substantial differences by race/ethnicity and sex, respectively. An escalating incidence during the last decades all over the globe has been reported [2]. This phenomenon is mainly due to an increase in micropapillary (<2 cm) histotype, while there is no substantial change in the incidence of the less common histological categories: follicular, medullary and anaplastic cancers. The increase is attributable to better detection of small papillary carcinomas as a result of improved diagnostic accuracy (neck ultrasound, US and fine needle aspiration cytology, FNAC). It is common experience in thyroid cancer referral centers that nearly 60%–80% of thyroid carcinomas detected nowadays are micropapillary thyroid carcinomas (<1 cm in size) carrying an excellent long-term prognosis [3]. However, more recently, an increased incidence for all size of thyroid tumor has been reported in the USA. During 1997– 2005, the annual percentage change (APC) for primary tumor <1.0 cm was 9.9 in man and 8.6 in women. A substantial increase was also observed for tumor >4 cm among men (1988–2005: APC 3.7) and women (1988–2005: APC 5.7) [4]. These data suggested that increased diagnostic scrutiny is not the only explanation, and environmental influence should also be considered. The only established environmental risk factor for thyroid carcinoma is exposure to ionizing radiation, and the risk, particularly of papillary carcinoma, is greater in subjects of younger age at exposure. An increased incidence of thyroid cancer in children and adolescents was observed in Ukraine, Belarus and certain regions of Russia as early as 4 years after the Chernobyl accident. The pre-Chernobyl incidence of thyroid cancer in Ukrainian children was very low (0.5–1.0 per 1 000 000 children). Following the explosion of the Chernobyl nuclear reactor in 1986, a dramatic increase in the incidence of benign and malignant thyroid tumors (80 times more) was observed in children born or conceived around the time of the accident in a wide area surrounding the reactor [5]. Despite increasing incidence, the mortality from thyroid cancer has tended to decline over the last three decades. It is unclear how much of the decline in mortality is due to better diagnosis rather than to improved treatment of thyroid neoplasm. The age-adjusted death rate was 0.5 per 100 000 men and women per year, increasing from 0.1% under age 20%–30% in the seventh and the eighth decades [2].