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  • A total of eight cancers (hepatocellular carcinoma, thyroid cancer, colorectal cancer, gastric cancer, lung cancer, prostate cancer, breast cancer, and cervical cancer) were included in the present study. We used data from the Korea Central Cancer Registry (KCCR) of the National Cancer Center Korea. More than 190 hospitals participate in the KCCR, and data regarding over 90% of newly diagnosed cancers in Korea are collected [17]. The KCCR offers annual national cancer incidence, survival, and prevalence data, and the KCCR database includes information regarding patients with cancer, such as sex, age, and date of diagnosis [4]. From the KCCR, we obtained the number of cancer patients by sex, age, and severity level from 2006 to 2013, as well as follow-up data for mortality for up to eight years. Furthermore, we utilized mid-year population data based on resident registration from the Korean Statistical Information Service of Statistics Korea to calculate incidence rates and prevalence rates [18]. The severity level was classified by SEER stage as follows: localized stage, regional stage, distant stage, and unknown stage. The SEER stage was based on the time of diagnosis. First, we described the number of incident cancer cases according to sex and SEER stage from 2006 to 2013. The incidence rates by sex and SEER stage were determined as the number of incident cancer cases by sex and SEER stage divided by the mid-year population by sex. The means of incidence rates and their 95% confidence intervals from 2006 to 2013 according to Poisson distribution assumption were estimated by type of cancer, sex, and SEER stage. Furthermore, we conducted statistical tests for linear trend of overall incidence rates and proportions of incidence rates by stage. Patients with cancer identified in 2006 underwent follow-up for all-cause mortality and observed survival rates by sex and SEER stage. All-cause mortality and observed survival rates by sex and SEER stage in each follow-up year were calculated as the number of patients with cancer alive by sex and SEER stage in each follow-up year divided by the total number of patients with cancer by sex and SEER stage in 2006. Finally, we estimated the prevalence rates for eight cancers by sex and SEER stage in 2011, 2012, and 2013. Fig 1 shows the method of estimating the number of prevalent cases. We assumed that patients with cancer who lived more than five years past their diagnosis were recovered from the cancer, and these patients were excluded from the prevalent cases. For example, prevalent cases in 2013 included the patients with cancer who were diagnosed in 2013, as well as patients with cancer who were diagnosed since 2009 and still alive (Fig 1). As with incidence rates, the 5-year prevalence rates by sex and SEER stage were calculated as the number of prevalent cases by sex and SEER stage divided by the mid-year population by sex. Figure data removed from full text. Figure identifier and caption: 10.1371/journal.pone.0203110.g001 Method of estimating prevalent cases. In the case of breast cancer, we only analyzed the female patients, because male patients account for a small proportion of the total patients with breast cancer. For a similar reason, all analyses were restricted to individuals aged ≥ 30 years. In particular, in the case of prostate cancer, only individuals aged ≥ 50 were included in the analyses, because prostate cancer patients under age 50 are rare in Korea. We used Microsoft Office Excel 2010 and Stata software (Stata/SE 13.1) for all analyses. In this study, P-values less than 0.05 were regarded statistically significant. Ethical approval and consent to participate were unnecessary because we used publicly available data without any personal identifiers.
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