Increasing Incidence of Chronic Lymphocytic Leukemia in Korea, 1999-2010: Comparison to Plasma Cell Myeloma
Authors: Lee Seung Jun , Tien Hwei-Fang , Park Hyeon Jin , Kim Jung-Ah , Lee Dong Soon 
Published: October 2019

Abstract
Introduction: Chronic lymphocytic leukemia (CLL) and plasma cell myeloma (PCM) have markedly higher incidences in Western compared with Asian countries. In Asian countries, both CLL and PCM have increased over the previous few decades. However, the epidemiologic characteristics of CLL have not been previously studied in Korea. To track the changing trends in the incidence of CLL and PCM, we investigated epidemiologic data in Korea from 1999 to 2010 and compared it with data regarding Taiwanese and Caucasian Americans. We specifically addressed the differences in the trends of CLL and PCM.
Methods: We included patients diagnosed with CLL or PCM between 1999 and 2010 from the KCCR and between 1992 and 2010 from the SEER database. We utilized the International Classification of Diseases for Oncology 3rd edition (ICD-O-3) codes for CLL (9823/3) and PCM (9732/3). The age at diagnosis was classified into 18 age groups by 5-year intervals. The data of Taiwan was obtained by personal communication.
Results: The ASR of CLL from 1999 to 2010 in Korea was 0.13/100,000 person-years (0.17/100,000 for men and 0.09/100,000 for women). The APC in the CLL incidence in Korea was 4.17% (95% CI: 0.77-7.68%) (Table 1). For comparison, the ASR of the CLL in the US from 1999 to 2010 was 3.21/100,000, and CLL exhibited an APC of 0.68% (95% CI: -0.39 to 1.77%). The APC of CLL over the previous 12 years in Korea (4.17%) was markedly higher (i.e., 6.1-fold) compared with the US (0.68%). In a comparison of different ethnic groups, the ASR in Caucasians was 3.57/100,000; this incidence was the highest rate observed (Figure 1). The ASRs in individuals of African descent and Asians/Pacific Islanders were 2.41/100,000 and 0.74/100,000, respectively. The temporal trends in the ASRs in all races remained stable.
The ASR of PCM for the period from 1999 to 2010 in Korea was 1.23/100,000 person-years (1.51/100,100 for men and 1.04/100,000 for women). The APC in the PCM incidence rates was 4.68% (95% CI: 4.12-5.24%) (Table 1). The ASR of PCM in the US from 1999 to 2010 was 3.97/100,000, which was 3.2-fold higher compared with Korea. The incidence of PCM in the US increased, with an APC of 0.50% (95% CI: 0.11-0.88%). The APC in Korea during the same period was 9.4-fold higher compared with the US. In the US, differences in the incidence were observed among ethnic groups, including Caucasians, African Americans and Asians or Pacific Islanders (Figure 1). African Americans constituted the group most susceptible to PCM, with an ASR of 8.42/100,000. The ASRs for Caucasian and Asians/Pacific Islanders were 3.67/100,000 and 2.37/100,000, respectively. The ASRs for the all races remained stable.
Conclusion: In conclusion, the incidence rates of CLL have gradually increased from 1999 to 2010, while those of PCM have increased steeply. Both of them still show prominent lower incidences compared to US, but the incidence rates of CLL and PCM appears to be stable in the US. Though genetic background is the key factor for ethnic difference in the incidence, further study will be needed to elucidate the reason for recent differential increasing trends between CLL and PCM incidence in Korea.
Table 1. Comparison of incidence and trend in CLL and PCM during 1999-2010 between US and Korea °° °° US Korea Comparison (US/Korea) CLL ASR* 3.21 0.13 24.69 APC (95% CI) 0.68 (-0.39 to 1.77) 4.17 (0.77 to 7.68)¢" 0.16 PCM ASR* 3.97 1.23 3.23 °° APC (95% CI) 0.50 (0.11 to 0.88)¢" 4.68 (4.12 to 5.24)¢" 0.11 * ASR are expressed per 100,000 person-years ¢" APC is statistically significantly different from zero Abbreviation: CLL, chronic lymphocytic leukemia; PCM, plasma cell myeloma; ASR, age-standardized rate; APC, annual percentage change; CI, confidence interval.
Figure 1. The age-standardized incidence rates of (A) chronic lymphocytic leukemia and (B) plasma cell myeloma in US, Taiwan, and Korea Abbreviation: W, White; B, Black; API, Asian/Pacific Islander. Figure 1. The age-standardized incidence rates of (A) chronic lymphocytic leukemia and (B) plasma cell myeloma in US, Taiwan, and Korea. / Abbreviation: W, White; B, Black; API, Asian/Pacific Islander.

Disclosures
No relevant conflicts of interest to declare.