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Cancer Statistics in Korea : Incidence , Mortality , Survival , and Prevalence in 2019

Purpose
The current study provides national cancer statistics and their secular trends in Korea, including incidence, mortality, survival, and prevalence in 2019.


Materials and Methods
Incidence, survival, and prevalence rates of cancer were calculated using the Korea National Cancer Incidence Database, from 1999 to 2019, with survival follow-up until December 31, 2020. Deaths from cancer were assessed using causes-of-death data obtained from Statistics Korea.


Results
In 2019, newly diagnosed cancer cases and deaths from cancer were reported as 254,718 (ASR, 275.4 per 100,000) and 81,203 (ASR, 72.2 per 100,000), respectively. For the first time, lung cancer (n=29,960) became the most frequent cancer in Korea, excluding thyroid cancer. The overall cancer incidence rates increased by 3.3% annually from 1999 to 2012, and decreased by 5.3% annually from 2012 to 2015, thereafter, followed by nonsignificant changes. The incidence of thyroid cancer increased again from 2016 (annual percentage change, 6.2%). Cancer mortality rates have been decreasing since 2002, with more rapid decline in recent years (annual decrease of 2.7% from 2002 to 2013; 3.3% from 2013 to 2019). The 5-year relative survival between 2015 and 2019 was 70.7%, which contributed to prevalent cases reaching over 2 million in 2019.


Conclusion
Cancer survival rates have improved over the past decades, but the number of newly diagnosed cancers is still increasing, with some cancers showing only marginal improvement in survival outcomes. As the number of cancer survivors increases, a comprehensive cancer control strategy should be implemented in line with the changing aspects of cancer statistics.


Introduction
It is estimated that there were approximately 19.3 million new cancer cases and 10 million deaths from cancer worldwide in 2020 [1]. During this century, cancer is expected to surpass cardiovascular disease as the leading cause of premature death in most countries [2].
Cancer is the leading cause of death in Korea [3]. In order to reduce the pain and social burden caused by cancer and to promote public health, the National Plan for Cancer Control has been implemented since 1996, and the 4th stage is in effect from 2021. As a fundamental part of the Plan, the Korea Central Cancer Registry publishes cancer registration statistics every year. The current study reports the most recent nationwide statistics on cancer incidence, survival, prevalence, and mortality, and their temporal trends.

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 Korea Central Cancer Registry (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 [4]. Completeness is an important indicator of data quality, and the 2019 KNCI DB was estimated to be 98.3% complete using the method proposed by Ajiki et al. [5]. CANCER RESEARCH AND TREATMENT (CRT) 4 Korean Cancer Association This article is protected by copyright. All rights reserved.
Annual mid-year population data and recently updated mortality data including causes of death from 1983 were obtained from Statistics Korea [3]. 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.

Cancer classification
All cancer cases had been registered in accordance with the International Classification of Diseases for Oncology, 3rd edition (ICD-O-3) [6]. 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 2019 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) [7].
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 [8], and the latter was the taxonomy used in "Cancer Incidence in Five Continents" [9], and both of them were provided by the 5 Korean Cancer Association This article is protected by copyright. All rights reserved.
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) [10] was used to categorize the extent of tumor invasion or metastasis.

Statistical analyses
Incidence, mortality, and prevalence rates were expressed as crude rates (CRs) or agestandardized 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

Incidence
In 2019, a total of 254,718 people were newly diagnosed with cancer in Korea, of which 52.7% (134,180 cases) were men and 47.3% (120,538 cases) were women ( Table 1). The five most diagnosed cancers in Korea were thyroid, lung, stomach, colorectal, and breast cancers; in men, lung and stomach cancers were followed by colorectal, prostate, and liver cancers, whereas breast and thyroid cancers were followed by colorectal, stomach, and lung cancers in women. These top five cancers in each sex accounted for 63.8% and 65.7% of all cancer cases in men and women, respectively. 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 in 2019. Excluding thyroid cancer, it is the first time in 2019 that lung cancer has surpassed stomach cancer to rank first in the incidence rate in Korea. Table 2 provides the CRs and ASRs of cancer incidence in 2019. The CR and ASR of all cancer 7 Korean Cancer Association This article is protected by copyright. All rights reserved. incidence were 496.2 per 100,000 (523.9 for men and 468.5 for women) and 275.4 per 100,000 (296.6 for men and 267.4 for women), respectively. The difference between 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 37.9%, under the condition that one survives to the age that matches the life expectancy of the Korean population. That probability was higher in men (39.9%) than in women (35.8%) (data not shown).
There were marked differences in age-specific incidence rates (Fig. 1). In the childhood population (0-14 years), leukemia, brain and central nervous system (CNS) cancer, and non-Hodgkin lymphoma were the top three cancers in both sexes, accounting for 31.3%, 14.7%, and 13.9% 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 52.1% of all cancers diagnosed. The most common cancers in that age group, excluding thyroid cancer, were leukemia and colorectal cancer 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 lung cancers (collectively accounting for 52.5%), while breast and thyroid cancers were the most common in women (collectively accounting for 54.8%). 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).

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Mortality
Since the causes-of-death statistics were published in 1983, cancer has been the number one cause of death in Korea. As of 2019, a total of 81,203 people (61.9% men and 38.1% women) died of cancer, accounting for 27.5% of all deaths in Korea (Tables 1 and 3). The overall CR for cancer deaths was 158.2 per 100,000, and the rate was approximately 1.6 times higher for men than for women (Table 4). Lung cancer was the leading cause of cancer death in both sexes (CR, 53.5 per 100,000 in men and 19.0 per 100,000 in women), followed by liver and colorectal cancers in men, and colorectal and pancreatic cancers in women. When stratified according to the age at the time of death, the most common causes of cancer mortality in both sexes were as follows: leukemia in their 10s and 20s, breast cancer in their 30s, liver cancer in their 40s and 50s, and lung cancer among those 60 years old or older (data not shown).

Trends in cancer incidence and mortality
Changes in cancer incidence rates from 1999 to 2019 and mortality rates from 1983 to 2019 are depicted in Fig. 3. Compared to 1999, cancer incidence rates increased about 29.8% and mortality rates decreased about 37.3%, in 2019 ( Table 5). The overall cancer incidence rates These trends were observed similarly in both men and women, although the slopes of change were much more pronounced in women for incidence, and in men for mortality rates (S1 and S2 Tables).

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cancers, and that of some male or female reproductive organs (ovary, corpus uteri, prostate, and testis) have been continuously increasing. In both sexes combined, breast (especially for women) and kidney cancers displayed initial rapid increases and then lessened increases after  (Table 5). These trends were observed similarly in both men and women, except for breast cancer in men and bladder cancer in women that revealed partially different results of trends from those described above. In men, decreasing trend of stomach, lung, and liver cancer throughout the period and colorectal cancer since 2011 were significant while prostate and kidney cancer had an increasing trend. In women, stomach, colorectal, liver, and cervix cancer had decreasing trend while breast and lung cancer revealed an increasing trend. The characteristic trend of thyroid cancer which changed rapidly in a short period of time, was more pronounced in women than in men (Fig. 4, S1 and S2 Tables).
The ASRs for mortality in most cancers have shown decreasing trends in Korea.
Stomach cancer revealed continuous decreasing trends throughout the entire observed period for mortality, with more pronounced decreasing slopes in more recent periods. Liver and lung Korean Cancer Association This article is protected by copyright. All rights reserved.
cancer mortality rates began to decrease in 2002 and 2001, respectively, followed by further rapid decreases starting in 2014. On the other hand, the mortality rates of colorectal, cervical, and thyroid cancers initially increased significantly until 2003; since then, the mortality rate from cervical cancer and thyroid cancer has decreased, and colorectal cancer has shown insignificant changes for 10 years and started to decrease from 2012 (Table 5). These trends were observed similarly in both sexes. However, breast cancer in women displayed significantly increasing mortality trends throughout the entire observed period, with less increasing trend after 2005 (Fig. 5, S1 and S2 Tables).

Survival rates
Over the past two decades, when cancer survival statistics have been compiled, the relative survival rates of cancer patients have increased significantly and steadily. The 5-year relative survival rates for all patients diagnosed with cancer in the recent five years, from 2015 to 2019 were 70.7% in both sexes; 64.5% in men and 77.3% in women ( Table 6). The temporal increasing trends in survival rates, from 42.9% in 1993-1995 to 70.7% in 2015-2019, were maintained even after excluding thyroid cancer (from 41.2% in 1993-1995 to 66.5% in 2015-2019), which has an excellent prognosis with a 5-year relative survival rate of 100%.
After thyroid cancer, survival rates were the highest for testis and prostate cancers in men (95.0% and 94.4%, respectively) and breast cancer in women (93.6%). On the contrary, the survival rates were the lowest for cancers of the pancreas (13.9%), and gallbladder plus other and unspecified parts of the biliary tract (28.5%) in both sexes. Stomach cancer (both sexes), prostate cancer (men), lung cancer, and leukemia (women) were associated with outstanding improvements in survival rates over the observed period. In contrast, advances have been slow for cancers of the brain and CNS, pancreas in both sexes. Korean Cancer Association This article is protected by copyright. All rights reserved.
In terms of stage distribution at diagnosis and recent survival rates according to the SEER summary stage in each cancer, Fig. 6

Prevalence rates
The total prevalent cancer cases in 2019 (identified as survivor at the time of January 1, 2020) were 2,147,503, surpassing 2 million since 2018 ( of, or one in ten, women) would have experienced cancer (data not shown). 100,000) and colorectal cancer (CR, 544.9 per 100,000). Prostate cancer in men and breast cancer in women revealed the highest prevalence rates (CR, 425.1 and 1,003.5 per 100,000, respectively).
The number of prevalent cases for common cancers, according to the time since cancer diagnosis, are described in Fig. 7. In total, 1,268,265 (59.1% of all prevalent cases) had survived > 5 years after cancer diagnosis, majority of them being survivors of thyroid, stomach, colorectal, and breast cancers. Another 462,265 (21.5% of all prevalent cases) have been alive 2-5 years after their cancer diagnosis, in which period they need regular follow-up; and the rest were 416,973 (19.4% of all prevalent cases) for whom it had been < 2 years since their cancer diagnosis, in which period they still need active cancer treatment.

Conclusion
Since 2015, the number of new cancer patients in Korea has been increasing, but the ASRs of incidence did not reveal a significant change. In 2019, lung cancer has surpassed stomach cancer to rank first in the incidence rate for the first time, excluding thyroid cancer.
During the past decade, the incidence of stomach, colorectal, liver, and cervical cancer has been declining while that of prostate and breast cancer have been on the rise since 1999. Thyroid cancer, which has decreased since 2012, has shown an increasing trend since 2015. The 5-year relative survival rate of cancer patients diagnosed in the past 5 years was 70.7%, which is steadily improving. Since 2018, the number of cancer survivors has exceeded 2 million, of Korean Cancer Association This article is protected by copyright. All rights reserved. https://gco.iarc.fr/today/data-sources-methods.

Korean Cancer Association
This article is protected by copyright. All rights reserved.  APC, annual percentage change; CNS, central nervous system. APC was calculated using age-standardized incidence data based on the Segi's world standard population. a) Significantly different from zero (p < 0.05). b) Includes the gallbladder and other/unspecified parts of the biliary tract.

Korean Cancer Association
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