The spatio-temporal distribution and risk factors of thyroid cancer during rapid urbanization-A case study in China

Incidences of thyroid cancer (TC) have been increasing worldwide in recent decades. In this research, we aimed to analyze the spatiotemporal pattern of TC and explore relevant environmental risk factors in Hangzhou (HZ), which is rapidly urbanizing and home to the highest TC incidence in China.

Spatial scan statistic was employed to analyze the spatiotemporal pattern of TC in HZ from 2008 to 2012. The geographically weighted regression model (GWR) was implemented to explore environmental risk factors. Its performance was compared to the traditional ordinary least squares model (OLS).

A total of 7147 TC cases (5385 female and 1762 male) were diagnosed in HZ from 2008 to 2012. High TC clusters were detected in the northeast, urban areas and expanded outwards while low clusters were located in the southwest rural areas. The GWR model generally performed better than the OLS in analyzing the associations between TC incidence and environmental factors. The industrial density, chemical oxygen demand of wastewater (COD) and the percentage of building area had a strong positive influence on the TC in the northeastern suburb areas of HZ, while the elevation, slope and the percentage of forest area had a significant negative correlation with TC in the middle, rural areas of HZ. Meanwhile, the accessibility to health care might have an impact on the TC incidence.

High clusters were mostly located in the northeastern urban areas and showed an expansion process from the center urban area to the suburb area, especially for female TC. Intensive industrial activities and the emission of organic pollutants, which positively correlated with the high TC clusters in the northeast suburb areas of HZ, should get proper attention.