Geospatial and Temporal Analysis of Thyroid Cancer Incidence in a Rural Population.
BACKGROUND
The increasing incidence of thyroid cancer has resulted in the rate tripling over the past 30 years. Reasons for this increase have not been established. Geostatistics and geographic information system (GIS) tools have emerged as powerful geospatial technologies to identify disease clusters, map patterns and trends, and assess the impact of ecological and socioeconomic factors (SES) on the spatial distribution of diseases. In this study, these tools were used to analyze thyroid cancer incidence in a rural population.


METHODS
Thyroid cancer incidence and socio-demographic factors in Vermont (VT), United States, between 1994 and 2007 were analyzed by logistic regression and geospatial and temporal analyses.


RESULTS
The thyroid cancer age-adjusted incidence in Vermont (8.0 per 100,000) was comparable to the national level (8.4 per 100,000), as were the ratio of the incidence of females to males (3.1:1) and the mortality rate (0.5 per 100,000). However, the estimated annual percentage change was higher (8.3 VT; 5.7 U.S.). Incidence among females peaked at 30-59 years of age, reflecting a significant rise from 1994 to 2007, while incidence trends for males did not vary significantly by age. For both females and males, the distribution of tumors by size did not vary over time; ≤1.0 cm, 1.1-2.0 cm, and >2.0 cm represented 38%, 22%, and 40%, respectively. In females, papillary thyroid cancer (PTC) accounted for 89% of cases, follicular (FTC) 8%, medullary (MTC) 2%, and anaplastic (ATC) 0.6%, while in males PTC accounted for 77% of cases, FTC 15%, MTC 1%, and ATC 3%. Geospatial analysis revealed locations and spatial patterns that, when combined with multivariate incidence analyses, indicated that factors other than increased surveillance and access to healthcare (physician density or insurance) contributed to the increased thyroid cancer incidence. Nine thyroid cancer incidence hot spots, areas with very high normalized incidence, were identified based on zip code data. Those locations did not correlate with urban areas or healthcare centers.


CONCLUSIONS
These data provide evidence of increased thyroid cancer incidence in a rural population likely due to environmental drivers and SES. Geospatial modeling can provide an important framework for evaluation of additional associative risk factors.
1 Department of Civil and Environmental Engineering, School of Engineering, University of Vermont , Burlington, Vermont.
John P
JP
Hanley
2 Department of Biology, College of Arts and Sciences, University of Vermont , Burlington, Vermont.
Erin
E
Jackson
3 Rubinstein School of Environment and Natural Resources, University of Vermont , Burlington, Vermont.
Leslie A
LA
Morrissey
1 Department of Civil and Environmental Engineering, School of Engineering, University of Vermont , Burlington, Vermont.
Donna M
DM
Rizzo
4 Department of Surgery, College of Medicine, University of Vermont , Burlington, Vermont.
Brian L
BL
Sprague
5 Center for Clinical and Translational Science and Department of Microbiology and Molecular Genetics, College of Medicine, University of Vermont , Burlington, Vermont.
Indra Neil
IN
Sarkar
6 Department of Pharmacology, College of Medicine, University of Vermont , Burlington, Vermont.
Frances E
FE
Carr
D018263:Adenocarcinoma, Follicular / Q000453:epidemiology* / Q000473:pathology; D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D002277:Carcinoma / Q000453:epidemiology* / Q000473:pathology; D018278:Carcinoma, Neuroendocrine / Q000453:epidemiology* / Q000473:pathology; D002291:Carcinoma, Papillary; D002648:Child; D005260:Female; D006801:Humans; D015994:Incidence; D016014:Linear Models; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D012424:Rural Population / Q000706:statistics & numerical data*; D017678:Sex Distribution; D062211:Spatio-Temporal Analysis; D000077273:Thyroid Cancer, Papillary; D065646:Thyroid Carcinoma, Anaplastic / Q000453:epidemiology* / Q000473:pathology; D013964:Thyroid Neoplasms / Q000453:epidemiology* / Q000473:pathology; D047368:Tumor Burden; D014707:Vermont / Q000453:epidemiology; D055815:Young Adult