Accounting for Immigrant Status when Calculating Cancer Incidence Rates for Bangkok

Abstract

Objective: Cancer-registry data are crucial for definingcancer incidence rates for use in setting service priorities<br />and monitoringservice effects. This applies in Thailand where cancer is the leading cause of death and service needs<br />are high. The Bangkok Cancer Registry (population-based) was established in 1990to determine cancer incidence rates<br />for Bangkok. This proved difficult, however, because the Bangkokpopulation (>8million) fluctuates with numbers of<br />temporary visitors, many of whom visit Bangkok temporarily for services. If these visitors are mis-categorized as<br />usual residents, cancer incidence rateswould be inflated. During 2013-2015, residential addresses on the Registry<br />were cross-checked against official addresses on the National Civil Registration records of the Ministry of Interior.<br />The effectsof this cross-checking on incidence rates are discussed. Methods: Residential addresses recorded on<br />the Registry for cancer diagnoses in 2013-2015 were corrected using official Ministry data. Effects on numbers of<br />recorded cancers and crude and directly age-standardized rates (World Population) were determined. Results: Of 44,813<br />cancer casesdiagnosed and recorded on the Registryduring 2013-2015, 36,327 (81.1%) had an official Bangkok<br />address. When limiting analyses to these cases, the crude incidencefor all cancer sites combined reduced by 18.9%<br />(19.7% for males and 18.3% for females). Corresponding reductions in age-standardized incidence rates were 20.0%<br />for males and 18.8% for females. These reductions varied for common cancer sites:in males,from 14.8% for lung to<br />25.9% for colorectal cancer; and in females, from 12.9% for lung to 24.0% for cervical cancer. Conclusions: These<br />differences are considered sufficient in magnitude to justifyroutine use of official residential data when calculating<br />cancer incidence rates for Bangkok. If these rates are to be compared with comparable rates for other Asian citiesthat<br />serve broader populations, equivalent methodologies for determining residential status would be needed for all cities.