Improved detection does not fully explain the rising incidence of well-differentiated thyroid cancer: a population-based analysis

Abstract

Background: The increasing incidence of thyroid cancer may be an artifact of increased diagnostic scrutiny, permitting detection of smaller, subclinical thyroid cancers. Our objective was to examine trends in the incidence of well-differentiated thyroid cancers with large size and adverse pathological features.

Methods: Detailed population-based analysis of incidence trends in well-differentiated thyroid carcinoma (1973-2006) in the Surveillance Epidemiology and End Results (SEER) cancer registry, using weighted least squares and Joinpoint regression models.

Results: The incidence of well-differentiated thyroid cancer (WDTC) in the United States has tripled since 1973 (P < .0001). Incidence trends differ significantly between geographic regions and racial groups. Large WDTCs, including those >4 cm or >6 cm, have more than doubled in incidence (P < .0001). Cancers with extrathyroidal extension and with cervical metastases have also more than doubled in incidence (P < .0001).

Conclusions: While the model of improving screening does explain increased diagnoses of small thyroid cancers, significant rises in the incidence of large cancers, and cancers with clinically significant pathological adverse features, are harder to explain. Alternative hypotheses, including a true increase in cancer incidence, would seem to merit exploration.

Figure 1. Trends in the incidence of thyroid cancer in men and women

(a) Incidence per 100,000 of WDTC in the entire population, and men and women (b) Joinpoint regression of incidence trends in the entire population, (c) men and (d) women.

Figure 2. Trends in the incidence of WDTC by race

(a) Joinpoint regression of incidence trend among (a) white, (b) black, (c) Hispanic, and (d) Asian/Pacific Islander individuals. Note that Hispanic ethnicity was not recorded prior to 1992, and that data is therefore limited to the 1992–2006 period.

Figure 3. Trends in the incidence of WDTC by primary tumor size

(a) Incidence per 100,000 of WDTC stratified by size. (b) Joinpoint regression of incidence trends in cancers larger than 4cm, (c) larger than 5cm, and (d) larger than 6cm.

Figure 4. Trends in the incidence of WDTC by adverse pathologic features

(a) Joinpoint regression of incidence trends in (a) cancers without extrathyroidal extension, (b) cancers with extrathyroidal extension, (c) cancers without cervical metastases (in patients >45 years old), and (d) cancers with cervical metastases (in patients >45 years old).