In this study, data were obtained from institutions and previous studies. The number of FL cases in Taiwan between 2008–2019 was obtained from the Cancer Registry Annual Report of the Health Promotion Administration, Ministry of Health and Welfare, Taiwan [20 ]. The annual population size for calculating incidence was obtained from the Department of Household Registration, Ministry of the Interior, Taiwan [21 ]. These annual reports were based on the Taiwan Cancer Registry Database (TCRD), a high-quality database from a nationwide population-based cancer registry system. In terms of the quality indicators of the registry, the completeness rates ranged from 91.3% in 2001 to 98.3% in 2019, the percentage of death certificate–only cases in all cancer cases (DCO%) decreased from 2.6% in 2003 to 0.7% in 2019, while the percentage of morphological verification (MV%) increased from 87.1% in 2003 to 93.5% in 2019 [15 (link),22 ,23 (link)].
Cases of patients with FL were identified using the International Classification of Disease for Oncology, Third Edition (ICD-O-3; Histology codes: 9690, 9691, 9695, and 9698) [20 ,24 ].
Age-standardized incidence rates (ASRs) and male-to-female incidence rate ratios (M/F IRRs) were calculated. ASR was age-adjusted to the 2000 world standard population as defined by the World Health Organization [25 ]. The temporal trends for the incidence of both sexes were described using the annual percent change (APC) calculated using the Joinpoint Regression Program, Version 4.9.1.0 (NCI Statistical Methodology and Applications Branch, Bethesda, MD, USA) [26 ]. The APCs were estimated by observing the changes in the trend on a log scale and assuming constant variance.
We further combined the data, based on the TCRD, in Taiwan between 2002–2007 as reported by Ko et al. [15 (link)] and compared the ASRs with those reported in Japan and South Korea. Japanese data were retrieved from Chihara et al. and the National Cancer Center, Japan, both of which are population-based cancer registry data [12 (link),27 ]. Korean data were obtained from Lee et al. and Kim et al.; the data were from the Korea Central Cancer Registry, (a hospital-based nationwide cancer registry) and from the National Health Information Database, (a public database that covered the entire Korean population), respectively [2 (link),13 (link)]. Based on the ASRs provided in these reports, we computed the APCs for the Japanese and Korean population.
An independent two-sided t-test was used to determine whether APC was statistically significant from zero. A p-value < 0.05 was considered statistically significant. Incidence rate ratios (IRRs) were calculated using the numbers of FL cases for each area and the age-specific population structure for each year. Statistical significance in difference between IRRs was determined whether the 95% confidence intervals (CIs) overlap between IRRs or not.
Cases of patients with FL were identified using the International Classification of Disease for Oncology, Third Edition (ICD-O-3; Histology codes: 9690, 9691, 9695, and 9698) [20 ,24 ].
Age-standardized incidence rates (ASRs) and male-to-female incidence rate ratios (M/F IRRs) were calculated. ASR was age-adjusted to the 2000 world standard population as defined by the World Health Organization [25 ]. The temporal trends for the incidence of both sexes were described using the annual percent change (APC) calculated using the Joinpoint Regression Program, Version 4.9.1.0 (NCI Statistical Methodology and Applications Branch, Bethesda, MD, USA) [26 ]. The APCs were estimated by observing the changes in the trend on a log scale and assuming constant variance.
We further combined the data, based on the TCRD, in Taiwan between 2002–2007 as reported by Ko et al. [15 (link)] and compared the ASRs with those reported in Japan and South Korea. Japanese data were retrieved from Chihara et al. and the National Cancer Center, Japan, both of which are population-based cancer registry data [12 (link),27 ]. Korean data were obtained from Lee et al. and Kim et al.; the data were from the Korea Central Cancer Registry, (a hospital-based nationwide cancer registry) and from the National Health Information Database, (a public database that covered the entire Korean population), respectively [2 (link),13 (link)]. Based on the ASRs provided in these reports, we computed the APCs for the Japanese and Korean population.
An independent two-sided t-test was used to determine whether APC was statistically significant from zero. A p-value < 0.05 was considered statistically significant. Incidence rate ratios (IRRs) were calculated using the numbers of FL cases for each area and the age-specific population structure for each year. Statistical significance in difference between IRRs was determined whether the 95% confidence intervals (CIs) overlap between IRRs or not.
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