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The medical insurance system of Beijing covers individuals who continuously worked or resided in the administrative area of Beijing, irrespective of place of household registration. In this study, we obtained data of the insured population in 2019 (covering about 20 million permanent residents and local employees) from the medical insurance administrative systems and extracted all the lymphoma-related medical claims records from January 1, 2012 to December 31, 2020, using both the International Classification of Diseases (tenth revision) (ICD-10) code (C81–85, C88, C90, C96) and text-based diagnosis (using a dictionary of lymphoma diagnosis constructed by reviewing the Chinese version of the ICD-10 and extracting all keywords indicating lymphoma cases) (7). The period between 2012 and 2018 was set as the 7-year time window for identifying prevalent cases in 2019, and the year 2020 was also included to avoid missing 2019 incident cases due to reimbursement delay (7). The standard procedure for identifying incident cancer cases (lymphoma) in 2019 has been described previously (Figure 1) (7). In brief, among the extracted claims records, those from primary or unrated healthcare facilities were excluded due to insufficient diagnostic qualifications (consistent with the criteria adopted in BCR). Lymphoma diagnoses were then determined using both ICD-10 codes and text-based diagnoses. When either was missing or inconsistency occurred, manual evaluation was performed through group discussion among 3 trained investigators specialized in lymphoma and/or epidemiology. For patients with multiple records, only the first one with definite lymphoma diagnosis was retained for each patient. Finally, the new records from January 1, 2019 to December 31, 2019 were kept, and the corresponding patients were defined as incident lymphoma cases in this study. The corresponding admission date of each lymphoma case was defined as its incidence date, which was in accordance with the BCR (10).
Figure 1.The procedure for capturing incident lymphoma cases in 2019 from the administrative systems of medical insurance in Beijing (MIS-CASS).
Abbreviations: ICD-10=International Classification of Diseases (tenth revision); MIS-CASS=Medical-Insurance-System-based Cancer Surveillance System.Out of regard for confidentiality, individual-level identifiable personal information (name, identity number, telephone number, home address, and so on) were masked, and a unique encrypted identification code was generated for each case in order to eliminate duplicate records.
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In this study, incidence rate generated from MIS-CASS referred to the number of new lymphoma cases occurring in a given year (2019) in the insured population in Beijing [see the following formula (11)].
$$ {{\rm{Incidence \; rate}}= \dfrac {{\rm{Number\; of \; new\; lymphoma \; cases}}} {{\rm{Insured}}\;{\rm{population}}\;{\rm{at}}\;{\rm{risk}}} \; {\rm{in}}\;2019} $$ Crude incidence rate, age-specific incidence rate, and age-standardized incidence rate (ASR) were calculated by gender and subtype. Lymphoma was generally categorized into Hodgkin lymphoma (C81), non-Hodgkin lymphoma (C82–85, C96), and multiple myeloma (C88, C90) (consistent with the method used for the BCR and other PBCRs in China), and was further subdivided when describing morphologic distribution. The China standard population in 2000 (ASR China) and the Segi standard population (ASR World) were applied for calculation of ASRs. We then compared MIS-CASS estimates of 2019 with the latest BCR-reported lymphoma incidence data of 2017 which was published in April, 2021 (12). This study was approved by the Institutional Review Board of the Peking University School of Oncology, China (No. 2019KT44).
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The lymphoma incidence in Beijing estimated by MIS-CASS was close to that reported by BCR (crude incidence rate: 9.8/100,000 vs. 10.6/100,000) (Table 1), and no significant difference in morphologic distribution was detected between MIS-CASS and BCR (Hodgkin lymphoma: 5.1% vs. 4.6%, non-Hodgkin lymphoma: 70.6% vs. 69.8%, multiple myeloma: 24.3% vs. 25.6%, P=0.559) (Figure 2) (12).
Surveillance approach Subtype ICD-10 of lymphoma Gender No. of cases Crude incidence rate (1/105) ASR China (1/105) ASR World (1/105) MIS-CASS All C81–85, C88, C90, C96 Both 2,002 9.8 6.8 6.6 Male 1,090 10.3 7.3 7.3 Female 912 9.3 6.3 5.9 Hodgkin lymphoma C81 Both 103 0.5 0.4 0.4 Male 48 0.5 0.4 0.3 Female 55 0.6 0.5 0.4 Non-Hodgkin lymphoma C82–85, C96 Both 1,413 6.9 4.8 4.7 Male 754 7.1 5.1 5.1 Female 659 6.7 4.5 4.3 Multiple myeloma C88, C90 Both 486 2.4 1.5 1.5 Male 288 2.7 1.8 1.8 Female 198 2.0 1.3 1.2 BCR* All C81–85, C88, C90, C96 Both 1,439 10.6 5.9 5.6 Male 814 12.0 6.8 6.6 Female 625 9.2 4.9 4.7 Abbreviations: MIS-CASS=Medical-Insurance-System-based Cancer Surveillance System; BCR=Beijing Cancer Registry; ICD-10=International Classification of Diseases (tenth revision); ASR China=age-standardized incidence rate by China standard population in 2000; ASR World=age-standardized incidence rate by world standard population (Segi population).
* The latest lymphoma incidence data of BCR (year of 2017) were derived from Beijing Cancer Registry Annual Report 2020 (12).Table 1. Comparison of the latest lymphoma incidence estimates in Beijing between MIS-CASS (2019) and BCR (2017).
Figure 2.Morphologic distribution of incident lymphoma cases in Beijing, 2019 (MIS-CASS). (A) Lymphoma (C81–85, C88, C90, C96); (B) Hodgkin lymphoma (C81); (C) Non-Hodgkin lymphoma (C82–85, C96); (D) Multiple myeloma (C88, C90).
Abbreviation: MIS-CASS=Medical-Insurance-System-based Cancer Surveillance System.However, the absolute number of new lymphoma cases identified by MIS-CASS was 39.1% higher than that reported by the BCR (2,002 vs. 1,439) (still 34.1% higher when only claims data from BCR-designated hospitals were included for analysis) (Table 1). Further analysis revealed that, among the 110 hospitals where the new lymphoma cases were diagnosed in 2019 according to MIS-CASS, only 90 were BCR-designated hospitals (12), and the remaining 20 hospitals contributed 22.2% of the excess patients (125/563). In addition, due to differences in target population between MIS-CASS (insured population) and BCR (household registered population), the population covered by MIS-CASS was 6.5 million larger than that for BCR in the age group of 20–49 years (Supplementary Figure S1).
Regarding age distribution, the incidence rate of lymphoma was relatively low in patients aged below 50 years and peaked at 75–84 years (Figure 3). The MIS-CASS-estimated number of new lymphoma cases peaked at age 60–69 years for both males and females, which was similar with the age distribution reported by the BCR, but was notably higher for the majority of the age groups, especially for men of 30–69 years and for women of 20–69 years (Figure 4).
Figure 3.Age-specific incidence rates of lymphoma by gender and subtype in Beijing, 2019 (MIS-CASS). (A) Lymphoma (C81–85, C88, C90, C96); (B) Hodgkin lymphoma (C81); (C) Non-Hodgkin lymphoma (C82–85, C96); (D) Multiple myeloma (C88, C90).
Abbreviation: MIS-CASS=Medical-Insurance-System-based Cancer Surveillance System.Figure 4.Comparison of the absolute number of new lymphoma cases by age group in Beijing between MIS-CASS (2019) and BCR (2017). (A) Including all designated medical insurance hospitals for MIS-CASS. (B) Including only BCR-designated hospitals for MIS-CASS.
Note: The latest lymphoma incidence data of BCR (year of 2017) were derived from Beijing Cancer Registry Annual Report 2020 (12). Abbreviations: MIS-CASS=Medical-Insurance-System-based Cancer Surveillance System; BCR=Beijing Cancer Registry.
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