Cancer Statistics in Korea: Incidence, Mortality, Survival, and Prevalence in 2020

Mee Joo Kang, 1, 2 Kyu-Won Jung, 1, 2 So Hyun Bang, 1, 2 Seo Hyun Choi, 1, 2 Eun Hye Park, 1, 2 E Hwa Yun, 1, 2 Hye-Jin Kim, 1, 2 Hyun-Joo Kong, 1, 2 Jeong-Soo Im, 3 Hong Gwan Seo, 1, 4 and The Community of Population-Based Regional Cancer Registries *

Mee Joo Kang

1 Korea Central Cancer Registry, National Cancer Center, Goyang, Korea

2 Division of Cancer Registration and Surveillance, National Cancer Control Institute, National Cancer Center, Goyang, Korea

Kyu-Won Jung

1 Korea Central Cancer Registry, National Cancer Center, Goyang, Korea

2 Division of Cancer Registration and Surveillance, National Cancer Control Institute, National Cancer Center, Goyang, Korea

So Hyun Bang

1 Korea Central Cancer Registry, National Cancer Center, Goyang, Korea

2 Division of Cancer Registration and Surveillance, National Cancer Control Institute, National Cancer Center, Goyang, Korea

Seo Hyun Choi

1 Korea Central Cancer Registry, National Cancer Center, Goyang, Korea

2 Division of Cancer Registration and Surveillance, National Cancer Control Institute, National Cancer Center, Goyang, Korea

Eun Hye Park

1 Korea Central Cancer Registry, National Cancer Center, Goyang, Korea

2 Division of Cancer Registration and Surveillance, National Cancer Control Institute, National Cancer Center, Goyang, Korea

E Hwa Yun

1 Korea Central Cancer Registry, National Cancer Center, Goyang, Korea

2 Division of Cancer Registration and Surveillance, National Cancer Control Institute, National Cancer Center, Goyang, Korea

Hye-Jin Kim

1 Korea Central Cancer Registry, National Cancer Center, Goyang, Korea

2 Division of Cancer Registration and Surveillance, National Cancer Control Institute, National Cancer Center, Goyang, Korea

Hyun-Joo Kong

1 Korea Central Cancer Registry, National Cancer Center, Goyang, Korea

2 Division of Cancer Registration and Surveillance, National Cancer Control Institute, National Cancer Center, Goyang, Korea

Jeong-Soo Im

3 National Cancer Control Institute, National Cancer Center, Goyang, Korea

Hong Gwan Seo

1 Korea Central Cancer Registry, National Cancer Center, Goyang, Korea

4 National Cancer Center Graduate School of Cancer Science and Policy, National Cancer Center, Goyang, Korea

2 Division of Cancer Registration and Surveillance, National Cancer Control Institute, National Cancer Center, Goyang, Korea

4 National Cancer Center Graduate School of Cancer Science and Policy, National Cancer Center, Goyang, Korea

Correspondence: Kyu-Won Jung, Korea Central Cancer Registry, National Cancer Center, 323 Ilsan-ro, Ilsandong-gu, Goyang 10408, Korea, Tel: 82-31-920-2015, Fax: 82-31-920-2179, E-mail: rk.er.ccn@ara

Chang-Hoon Kim (Busan Cancer Registry, Pusan National University Hospital), Cheol-In Yoo (Ulsan Cancer Registry, Ulsan University Hospital), Yong-Dae Kim (Chungbuk Cancer Registry, Chungbuk National University Hospital), Young-Taek Kim (Daejeon/Chungnam Cancer Registry, Chungnam National University and Hospital), Chul Min Park (Jeju Cancer Registry, Jeju National University and Hospital), Jung-Ho Youm (Chonbuk Cancer Registry, Jeonbuk National University Hospital), Kyu-Hyoung Lim (Kangwon Cancer Registry, Kangwon National University and Hospital), Nam-Soo Hong (Daegu/Gyeongbuk Cancer Registry, Kyungpook National University), Sun-Seog Kweon (Gwangju/Jeonnam Cancer Registry, Chonnam National University Hwasun Hospital), Woo-Chul Kim (Incheon Cancer Registry, Inha University Hospital), Ki-Soo Park (Gyeongnam Cancer Registry, Gyeongsang National University and Hospital).

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Associated Data

Abstract

Purpose

The current study provides national cancer statistics and their secular trends in Korea, including incidence, mortality, survival, and prevalence in 2020.

Materials and Methods

Incidence, survival, and prevalence rates of cancer were calculated using the Korea National Cancer Incidence Database, from 1999 to 2020, with survival follow-up until December 31, 2021. Deaths from cancer were assessed using causes-of-death data obtained from Statistics Korea.

Results

The number of new cancer diagnoses in 2020 decreased by 9,218 cases (3.6%) compared to 2019. In 2020, newly diagnosed cancer cases and deaths from cancer were reported as 247,952 (age-standardized rate [ASR], 262.2 per 100,000) and 82,204 (ASR, 69.9 per 100,000), respectively. The overall cancer incidence rates increased by 3.3% annually from 1999 to 2012, and decreased by 5.0% annually from 2012 to 2015, thereafter, followed by nonsignificant changes. Cancer mortality rates have been decreasing since 2002, with more rapid decline in recent years. The 5-year relative survival between 2016 and 2020 was 71.5%, which contributed to prevalent cases reaching over 2.2 million in 2020.

Conclusion

In 2020, the number of newly diagnosed cancer patients decreased due to the coronavirus disease 2019 pandemic, but the overall trend is on the rise. Cancer survival rates have improved over the past decades. As the number of cancer survivors increases, a comprehensive cancer control strategy should be implemented in line with the changing aspects of cancer statistics. The long-term impact of the coronavirus disease 2019 pandemic on cancer statistics needs to be investigated in the future.

Introduction

Cancer is one of the leading causes of death worldwide, with an estimated 19.3 million new cancer cases and 10 million deaths worldwide in 2020 [1]. In Korea, cancer has been the leading cause of death since 1983 [2]. In response to this public health threat, the National Plan for Cancer Control was implemented in 1996, and the 4th stage is in effect from 2021. As a fundamental part of the Plan, the Korea Central Cancer Registry (KCCR) publishes cancer registration statistics every year. In 2020, there was a negative impact on cancer diagnosis and treatment as medical use declined due to the coronavirus disease 2019 (COVID-19) pandemic. Reduced and delayed access to health care, including dec-reased cancer screening rates, was a phenomenon that has appeared not only in Korea but globally [3–5]. While short-term decreases in cancer incidence statistics are expected, it will take years to quantify the associations and consequences of these phenomenon, which is beyond the scope of this article [3]. In this study, we report the most recent nationwide statistics on cancer incidence, survival, prevalence, and mortality, and their temporal trends.

Materials and Methods

1. Data sources

Annual cancer statistics in Korea are calculated using a national and population-based database of cancer occurrence, the Korea National Cancer Incidence Database (KNCI DB). Every year, the KCCR collects information on patients diagnosed with cancer at hospitals across the country during the past year. The data from previous year is backed up with information compiled by central and 11 regional cancer registries, including information on cancer patients missed in hospital-based registrations. Hence, it takes two years to complete and calculate the year’s KNCI DB and cancer statistics. The KCCR has reported nationwide statistics since 1999; other detailed information on the KCCR and KNCI DB is provided in our previous report [6]. Completeness is an important indicator of data quality, and the 2020 KNCI DB was estimated to be 98.3% complete using the method proposed by Ajiki et al. [7].

Annual mid-year population data and recently updated mortality data including causes of death from 1983 were obtained from Statistics Korea [2]. To confirm the validity of individual vital statuses used in survival and prevalence calculation, the KNCI DB was linked to both mortality and population resident registration data, which were obtained from the Ministry of the Interior and Safety.

2. Cancer classification

All cancer cases had been registered in accordance with the International Classification of Diseases for Oncology, 3rd edition (ICD-O-3) [8]. The range of cancers to be registered and used for the national statistics calculation was limited to records with a behavior code of “/2 (carcinoma in situ)” or “/3 (malignant),” from the morphology (i.e., histology) codes of ICD-O-3, by which a patient was initially enrolled in the KNCI DB. Similar to previous reports, malignant cancer cases and their statistics were mainly assessed in this article. In addition, the supplementary incidence statistics for carcinoma in situ cases were also calculated separately, using 2020 KNCI DB.

For the convenience of classification and reporting, the ICD-O-3 codes were converted to the classification of the International Classification of Diseases, 10th edition (ICD-10) [9]. Exceptionally, some hematopoietic diseases (myeloproliferative disorders/myelodysplastic syndromes) are not classified as malignant cancer in ICD-10 classification, therefore their ICD-O-3 codes were used without any conversion. For mortality data, causes of death were coded according to the ICD-10.

We adopted cancer classifications with 24 and 61 types; the former was a modified classification based on the GLOBOCAN cancer dictionary [10], and the latter was the taxonomy used in “Cancer Incidence in Five Continents” [11], and both of them were provided by the International Association of Cancer Registries. In this article, cancer classification with 24 types of cancer was used for description. The summary staging system developed under the Surveillance, Epidemiology, and End Results (SEER) program (i.e., SEER summary staging) [12] was used to categorize the extent of tumor invasion or metastasis.

3. Statistical analyses

Incidence, mortality, and prevalence rates were expressed as crude rates (CRs) or age-standardized rates (ASRs) per 100,000 people. The CR was defined as the total number of newly diagnosed (for incidence) or deceased (for mortality) cases in a year divided by the mid-year population. The ASR was defined as the weighted average of the age-specific rates in which the weights represent the proportions of people in the corresponding age groups in a standard population [13]. ASRs were standardized using Segi’s world standard population [14]. The cumulative risk of developing cancer from birth to life expectancy during 2020 in Korea were also assessed, assuming no other cause of death (i.e., by simply calculating the sum of the age-specific cancer rates from birth to life expectancy), as follows [13]:

Cumulative risk of developing cancer from birth to life expectancy = 100 × ( 1 - e - cumulative rate 100 )

Trends in ASRs were estimated using Joinpoint regression, with a maximum number of two joinpoints. The results were summarized as annual percentage changes with the best model fit, based on a linear model for the natural log-transformed ASRs.

The survival rate of cancer patients, diagnosed between 1993 and 2020, was calculated based on the results of follow-up until December 31, 2021. The 5-year relative survival rate was defined as the ratio of observed survival of cancer patients to expected survival in the general population, adjusting the effects of other causes of death using the standard population life table provided by Statistics Korea [2]. Relative survival rates were estimated using the Ederer II method [15] with some minor corrections, based on an algorithm devised by Paul Dickman [16]. Trends in 5-year relative survival rates were evaluated as percent differences in survival rates between 1993–1995 and 2016–2020.

Results

1. Incidence

The number of new cancer diagnoses in 2020 decreased by 9,218 cases (3.6%) compared to 2019. In 2020, a total of 247,952 people were newly diagnosed with cancer in Korea, of which 52.7% (130,618 cases) were men and 47.3% (117,334 cases) were women ( Table 1 ). The five most diagnosed cancers in Korea were thyroid, lung, colorectal, stomach, and breast cancers; in men, lung and stomach cancers were followed by prostate, colorectal, and liver cancers, whereas breast and thyroid cancers were followed by colorectal, lung, and stomach cancers in women. These top five cancers in each sex accounted for 62.8% and 64.8% of all cancer cases in men and women, respectively. Among the five most diagnosed cancers, the decrease in new cancer diagnosis in 2020 compared to 2019 was the largest for stomach cancer (3,058 cases, −10.3%), followed by thyroid cancer (1,827 cases, −5.9%), and colorectal cancer (1,549 cases, −5.3%). Thyroid cancer was the most frequent cancer from 2010 to 2014: its ranking fell after the debate on overdiagnosis in 2014, but recently rose again and regained the first rank since 2019. Table 2 provides the CRs and ASRs of cancer incidence in 2020. The CR and ASR of all cancer incidence were 482.9 per 100,000 (510.1 for men and 455.8 for women) and 262.2 per 100,000 (279.1 for men and 257.3 for women), respectively. The difference bet-ween CR and ASR implies that majority of cancer patients in Korea belong to the elderly, as opposed to the world’s standard population, which has a higher proportion of young people. The overall lifetime probability of being diagnosed with any cancer was 36.9%, under the condition that one survives to the age that matches the life expectancy of the Korean population. That probability was higher in men (39.0%) than in women (33.9%) (data not shown).

Table 1

Cancer incidence, deaths and prevalence by sex in Korea, 2020

CNS, central nervous system.

a) Limited-duration prevalent cases on January 1, 2020. These are patients who were diagnosed between January 1, 1999 and December 31, 2020 and who were alive on January 1, 2021. Multiple primary cancer cases were counted multiple times,

Table 2

Crude and age-standardized cancer incidence rates by sex in Korea, 2020

CNS, central nervous system.

There were marked differences in age-specific incidence rates ( Fig. 1 ). In the childhood population (0–14 years), leukemia, non-Hodgkin lymphoma, and brain and central nervous system (CNS) cancer were the top three cancers in both sexes, accounting for 30.5%, 15.2%, and 12.9% of all cancer cases diagnosed in this age group, respectively. Thyroid cancer was the most common cancer in both sexes among the adolescent and young adult populations (15–34 years), accounting for 52.3% of all cancers diagnosed. The most common cancers in that age group, excluding thyroid cancer, were colorectal cancer and leukemia in men, and breast and cervical cancer in women. In the 35–64-year age group, men were most commonly diagnosed with stomach, colorectal, liver, and thyroid cancers (collectively accounting for 51.5%), while breast and thyroid cancers were the most common in women (collectively accounting for 54.6%). For those aged 65 years and above, lung and prostate cancers were the most common in men, while colorectal and lung cancers were the most common in women. Most cancers have shown to increase in incidence with age; the exceptions were thyroid cancer in both sexes and breast cancer in women, which showed the highest incidence in those in their 30–40s and 40–50s age groups, respectively ( Fig. 2 ).

The five common sites of cancer incidence by age group and sex in Korea, 2020. (A) Men. (B) Women. Numbers in the graph are age-specific incidence rates per 100,000. CNS, central nervous system.