The Thyroid and its Diseases
	Chapter 18                                                    HOME Thyroid Cancer Updated 7 June 2009  by  Furio Pacini, M.D., and Leslie J. De Groot, M.D.  TO OBTAIN A DOWNLOAD OF THIS CHAPTER IN PDF OR WORD FORMAT,  CLICK HERE

Presentation of this chapter is supported in part by Abbott Pharmaceuticals, makers of Synthroid.

Incidence and Distribution

The annual incidence of thyroid cancer varies considerably in different registries, ranging from 1.2-2.6 per 100,000 individuals in men and from 2.0-3.8 per 100,000 in women (92, 93). It is particularly elevated in Iceland and Hawaii, being nearly two times higher than in North European countries, Canada and the USA. In Hawaii, the incidence rate of thyroid cancer in each ethnic group is higher than that registered in their country of origin (94), and it is particularly common among Chinese males and Filipino females. Most of the differences are probably due to ethnic or environmental factors (such as spontaneous background radiation) or dietary habits (95), but different standards of medical expertise and health care may also play a role in the efficiency of cancer detection. The American Cancer Society indicated incidence in the USA of nearly 10/100,000 population in 2003. The reported incidence has been increasing at more than 5%/yr for a decade. Recorded incidence of thyroid cancer increased by 2.4 fold between 1973 and 2002.  This increase has been attributed to increased diagnosis of tumors measuring < 2cm in diameter, and has not been associated with an increase in mortality(95.1 ).Other analyses indicate that there has been an increase in both small and large tumors, and that the change represents a definite increased incidence (95.2) .A recent review reported an incidence rate of 7.1-8.8 cases/100,000 population in the USA (Golden SH, Robinson KA, Saldanha I, Anton B, Ladenson PW.Clinical review: Prevalence and incidence of endocrine and metabolic disorders in the United States: a comprehensive review. J Clin Endocrinol Metab. 2009 Jun;94(6):1853-78.)

In sharp contrast with these data concerning the incidence of clinical thyroid cancer, is the prevalence found in autopsy series or screening programs. Autopsy studies indicate a surprising frequency ranging from 0.01 to over 2.0% (96,97). A survey of consecutive autopsies at Grace-New Haven Hospital found 2.7% of thyroids to harbor unsuspected thyroid cancer (97). Another 2.7% had discrete benign adenomas, and nearly half showed nodularity. The high prevalence was attributed to careful examination of the gland, but probably also reflects a highly selected group of older patients dying in a hospital. Up to 6% of thyroid glands in autopsied adults in the United States, and over 20% in Japan, also harbor microscopically detectable foci of thyroid carcinoma, which are believed to be of no biologic significance. Altogether autopsy studies suggest that thyroid cancer is in many instances not diagnosed during life or is not the immediate cause of death. Both suggestions are in accord with the rather leisurely growth of the majority of thyroid tumors, especially the frequent small papillary types.

The annual mortality from thyroid cancer in 2003 was 5 per million for men and 6 per million for women (98). The discrepancy between incidence and mortality reflects the good prognosis for most thyroid cancers. Recent statistics suggest about 6 deaths /million in the USA.

A classification is given in Table 18-1.

Thyroid tumors are rare in children and increase in frequency in each decade. The variety of tumor is also related to age (v.i.). Carcinomas are three times as frequent in women as in men. In the past, it was generally believed that thyroid tumors were more frequent in areas of endemic goiter, and reports from Colombia and Austria support this association (99) (see Chapter 11). More recent studies suggest that in iodine deficient countries the number of nodules is increased and, as a consequence, also the number of thyroid cancers is increased (100). Surveys conducted in the United States found no relation between usual geographic residence and incidence of thyroid cancer. Secondary primary non-thyroidal cancers occur in slightly increased frequency (1.31 SIR) in patients who have had a primary thyroid tumor.  While this may in part be related to therapy (e.g.- RAI), it is believed that it also may represent a common genetic or environmental effect predisposing to tumors (100.1).Sandeep TC, Strachan MW, Reynolds RM, Brewster DH, Scelo G, Pukkala E, Hemminki K, Anderson A, Tracey E, Friis S, McBride ML, Kee-Seng C, Pompe-Kirn V, Kliewer EV, Tonita JM, Jonasson JG, Martos C, Boffetta P, Brennan P. Second primary cancers in thyroid cancer patients: a multinational record linkage study.J Clin Endocrinol Metab. 2006 May;91(5):1819-25