Background: Thyroid cancer incidence has continuously increased for decades and the causes of this increase are still controversial. The objective of this study was to examine if the increased trend is different among the different National Cancer Institute (NCI) Race/Ethnicity Groups (REGs) within the NCI surveillance epidemiology and end results database for the United States.
Methods: Using recent 13-year surveillance epidemiology and end results data, we described the specific incidence trend of thyroid cancer for the REGs by tumor size, tested the statistical significance of the trend of incidence, and estimated the annual percentage change (APC) and 95% confidence interval. In addition, we compared the difference of 5-year survival rate among the REGs.
Results: Papillary thyroid cancer incidence significantly increased over 13 years from 1992 to 2004 among the five major REGs. The estimated APC was 5.6% (95% confidence interval = 5.1%-6.1%, p < 0.01) for the non-Hispanic whites group, 4.3% (3.0-5.5, p < 0.01) for the Blacks group, 2.8% (1.5-4.2, p < 0.01) for the Hispanic whites group, 1.5% (0.5-2.5, p < 0.01) for the Asians group, and 1.1% (-2.2-4.6, p = 0.477) for the American Indians/Alaska Natives group, respectively. The APCs among the REGs were significantly different (Z = 7.89, p < 0.001). The upward incidence trend could be seen in all small or large tumors as well as in women or in men. The proportion of local staged thyroid cancer increased by 24% in the Blacks group, 14.4% in the Hispanic whites group, 14.3% in the non-Hispanic whites group, and only 4.0% in the Asians group between two periods of 1992-1996 and 2000-2004. Five-year survival rates of patients with papillary tumor were about 95%, but that of anaplastic tumor ranged from 5.6% to 11.4% among REGs.
Conclusion: The time trend of incidence of thyroid cancer is different among the different NCI REGs. Differences in diagnostic scrutiny may explain the differences in the REG-related trend, but this cannot easily explain the relatively small degree of increase in the trend in the Asian and the Indians/Alaska Natives groups nor can it explain the increase in the trend of large tumors that are likely to be discovered by self-palpation by patients.