Geospatial and Temporal Analysis Show Increased Thyroid Cancer Incidence in Rural Population

The incidence of thyroid cancer, which is now the most rapidly increasing endocrine malignancy, has been increasing at a rate of 3% to 5% per year, resulting in a near doubling in the past 30 years. Although improved detection and increased diagnosis have certainly played a role in the increasing incidence of thyroid cancer, other contributing factors have not yet been established.

With the emergence of geostatistics and geographic information system (GIS) tools, geospatial techniques have gained prominence as a way to use geolocated data to visualize, analyze, interpret, and map disease clusters, patterns, and trends, and as a method to assess the impact of ecological and socioeconomic factors on the spatial distribution of diseases. Together, these tools help to identify new drivers of public health concerns, which was one of the aims of a study at the University of Vermont.

“In this study, we postulated that geospatial and temporal analyses would reveal novel patterns of thyroid cancer incidence in a rural population,” said John P. Hanley, of the School of Engineering, College of Engineering and Mathematical Sciences at the University of Vermont in Burlington. Hanley made his comments at the Endocrine Society’s 97th Annual Meeting & Expo. For the study by Hanley and colleagues, the Vermont Department of Health provided data, including the year of initial diagnosis, age at diagnosis, gender, primary site of disease at diagnosis, histology code, histological grade, behavior code, size of tumor, postal code at diagnosis, year last contacted, vital status, and death place code, for the period 1994 to 2007.

The thyroid cancer incidence rate in rural Vermont was 8.0 per 100,000 and comparable to the national incidence rate of 8.4 per 100,000. However, the annual percentage change (APC) in rural Vermont was 8.3% compared with a nationwide APC of 5.7%. Similar to national estimates, about 3 times as many women as men were diagnosed with thyroid cancer (3.1:1 females to males), and 0.5 deaths occurred per 100,000 cases. For women, the thyroid cancer incidence peaked in the 30- to 59-year-old age group and rose significantly between 2001 and 2007, while the incidence of thyroid cancer in men did not vary significantly by age.

Tumor size did not vary over time for men or women, with 38% of tumors being <1.0 cm, 22% between 1 and 2 cm, and 40% >2.0 cm. For women, 89% of cases were papillary thyroid cancer (PTC), 8% were follicular thyroid cancer (FTC), 2% were medullary thyroid cancer (MTC), and 0.6% were anaplastic thyroid cancer. For men, 77% of cases were PTC, 15% were FTC, 1% were MTC, and 3% were ATC.

Using geospatial analyses, the data provided evidence of an increased incidence of thyroid cancer—including both large and small tumors&mdash;in a rural population and in both women and men.

&ldquo;Our data indicate that factors other than increased diagnostic scrutiny are drivers of the increase in thyroid cancer incidence. These data provide evidence of increased thyroid cancer incidence in a rural population that is likely due to environmental drivers and socioeconomic factors,&rdquo; Hanley concluded.

Geospatial modeling can provide an important framework for evaluation of additional associative risk factors. Future studies will focus on expanding these analyses to the household level and elucidating associated risk factors in nonrandom clusters of patients.

Carr FE, Hanley JP, Jackson E, et al. Geospatial and temporal analysis of thyroid cancer incidence in a rural population. Presented at the 2015 Endocrine Society Annual Meeting; March 5-8, 2015; San Diego, CA. Poster Board FRI-026.

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