Continued rapid increase in thyroid cancer incidence in california: trends by patient, tumor, and neighborhood characteristics

Abstract

Background: Thyroid cancer incidence is increasing worldwide. Incorporating 22 years of incidence data through 2009, we extend examination of these trends among a wide array of subgroups defined by patient (age, sex, race/ethnicity, and nativity), tumor (tumor size and stage), and neighborhood (socioeconomic status and residence in ethnic enclaves) characteristics, to identify possible reasons for this increase.

Methods: Thyroid cancer incidence data on 10,940 men and 35,147 women were obtained from the California Cancer Registry for 1988-2009. Population data were obtained from the 1990 and 2000 U.S. Census. Incidence rates and 95% confidence intervals (CI) were calculated and incidence trends were evaluated using Joinpoint regression to evaluate the timing and magnitude of change [annual percentage change (APC) and rate ratios].

Results: The incidence of papillary thyroid cancer continues to increase in both men (APC, 5.4; 95% CI, 4.5-6.3 for 1998-2009) and women (APC, 3.8; 95% CI, 3.4-4.2 for 1998-2001 and APC, 6.3; 95% CI, 5.7-6.9 for 2001-2009). Increasing incidence was observed in all subgroups examined.

Conclusions: Although some variation in the magnitude or temporality of the increase in thyroid cancer incidence exists across subgroups, the patterns (i) suggest that changes in diagnostic technology alone do not account for the observed trends and (ii) point to the importance of modifiable behavioral, lifestyle, or environmental factors in understanding this epidemic.

Impact: Given the dramatic and continued increase in thyroid cancer incidence rates, studies addressing the causes of these trends are critical. Cancer Epidemiol Biomarkers Prev; 23(6); 1067-79. ©2014 AACR.

Figure 1. Average annual age-adjusted thyroid cancer incidence rates (per 100,000) in California, by sex and histologic type

Papillary: solid line with diamonds; follicular: dashed line with squares; medullary: small dashed line with triangles; anaplastic: dotted & dashed line with circles; “not otherwise specified”: dotted line with squares. Annual percent change, 1988–2009 (unless otherwise specified), for men and women, respectively: papillary: 1988–98 1.1 and 1998–09 5.4*, and 1988–01 3.8* and 2001–09 6.3*; follicular: 0.0 and 1.2*; medullary 0.4 and 1.0; anaplastic −0.9 and 1.2; and “not otherwise specified” histology: 3.0* and 0.3. * denotes p<0.05.

Figure 2

Reduction in differences in average annual percent change by tumor size in females due to optimal allocation of unknown tumor sizes.