Cancer burden in China from 2006 to 2010

Introduction

Cancer is a major cause of death worldwide. As estimated by GLOBOCAN 2008, there were approximately 12.7 million new cancer cases and 7.6 million cancer deaths in 2008, mainly in less developed countries [1]. Owing to an increase in the elderly population, environmental pollution, and infection, cancer has become one of the main public health problems in China [2-4]. Its incidence and mortality rates have increased in the past decade in China, as is the case in other developing countries [5]. In 2009, there were 3.06 million new cases of cancer and 2.21 million deaths due to cancer in China; this translates to 6 new cases and 4 deaths per minute [6]. Cancer has been the leading cause of death in urban areas and the second leading cause of death in rural areas [5].

It is important to study the burden of cancer in terms of years lived with disease and years of life lost. The global burden of disease [6-8], first studied by the World Bank and Harvard University in 1990, provided a new metric-the “disability adjusted-life year” (DALY)-for quantifying disease burden. The DALY index comprehensively reflects and can be used to calculate the years of life lost because of premature death and the years lived with disability.

We used various indicators to assess cancer burden in terms of disease frequency and its severity. Incidence, mortality, potential years of life lost (PYLL), and DALYs were calculated from population data. The results of this study will be useful for formulating health policies and establishing priorities in health intervention program planning and will guide health and biomedical research and resource generation and expansion.

Materials and methods

Two aspects of the population burden of cancer were examined: disease frequency (how often the disease occurs [incidence and mortality]) and severity (how serious the disease burden is [PYLL and DALY]). Burden was examined for all cancers according to sex and area (urban or rural).

Data collection

The data collected and their sources were as follows: 1) mortality rates (2006-2010) for deaths due to all causes in China, the China Health Statistics Annuals [9-13]; 2) abridged life tables for 2010, the 2010 Chinese population census [14]; 3) 2006-2010 incidence and mortality rates for cancer, the 2008-2012 Chinese Cancer Registry Annual Report by the National Center for Cancer Registries [15-19]; and 4) 2007-2011 population data, the China Population and Employment Statistics Yearbook [14,20-22].

Analytical indices

PYLL is an estimate of the average years a person would have lived if he or she had not died prematurely [23]. It is, therefore, a measure of premature mortality and was calculated as follows:

PYLL (years) = ∑_{N = 1}dx (L - X) (1)

where L is life expectancy, X is the median age, and dx is the number of deaths. For life expectancy, we used 74.8 years (72.4 years for men and 77.4 years for women); these values were obtained from the China Health Statistics Annuals for 2011 [14].

The PYLL rate is the number of potential years of life lost per thousand people and was calculated as follows:

PYLL rate = PYLL ÷ N × 1000 (2)

where N is the minimum number of premature deaths.

DALY is the sum of years of life lost (YLL) and years lost due to disability (YLD) [21] and was calculated as follows:

DALY (years) = YLL + YLD (3)

YLL is the number of cancer deaths in a given group (age or place of residence in our study) multiplied by the remaining life expectancy (in years) of healthy individuals. The formula is as follows [24]:

YLL = Number of deaths × life espectancy at the age of death (4)

YLD is the number of cancer cases at each nonfatal disease phase multiplied by the mean duration of each phase. The product is multiplied by the disability weight [25] of the life-years to account for the severity of each event. The formula is as follows [26]:

YLD = Number of cases × time until remission or death × disability weight (5)

The DALY rate was calculated as follows:

DALY rate = DALY/N × 1000‰ (6)

The relative ratio of cancer burden stratified by age and place of residence was calculated as follows:

Relative ratio = Incidence in men (rural areas)/Incidencce in women (urban areas) (7)

Using this formula, we calculated the relative ratios for the incidence, mortality, and rates of PYLL and DALY in men versus women and in rural versus urban areas.

Analytical tools

DISMOD2 software (www.who.int/healthinfo/global_burden_disease/tools_software/en/) was used to calculate the average age of onset and duration of cancer. The template provided by the World Health Organization (available from http://www.who.int/entity/healthinfo/bodreferencedalycalculationtemplate.xls) was used to calculate DALYs.

Statistical methods

The chi-square test was used to compare incidence and mortality rates in men versus women and in rural versus urban areas. The Wilcoxon test was used to compare PYLLs and DALYs in men versus women and in urban versus rural areas. The data were analyzed using SPSS software for Windows, version 20.0 (SPSS Inc., Chicago, IL, USA), and a P value < 0.05 was considered to be statistically significant.

Results

Cancer incidence

The incidence rate of all cancers in the registration areas ranged from 303.84/100,000 in 2006 to 268.65/100,000 in 2010 for men and from 243.01/100,000 to 200.21/100,000 for women (Table 1). Incidence was approximately 1.2 times higher in men than in women (Figure 1A). The incidence rate was 285.97/100,000 in urban areas and 250.91/100,000 in rural areas (Table 1). The rural: urban incidence ratio decreased from 0.89 in 2006 to 0.69 in 2010 (Figure 1B).

Figure 1

Relative Ratio of cancer burden in china by sex and districts. A. Male: female ratios for incidence and mortality. B. Rural: urban ratios for incidence and mortality. C. Male: female ratios for PYLL and DALY rates. D. Rural:urban ratios for PYLL and DALY rates. RR, relative ratio.

Table 1

The incidence of cancer in China in 2006-2010

Year	All areas			Urban areas			Rural areas
	Men	Women	Both	Men	Women	Both	Men	Women	Both
2006	303.84	243.01	273.66	304.09	255.48	280.17	302.95	197.43	250.35
2007	305.22	246.46	276.16	305.76	263.2	284.71	303.65	197.41	251.07
2008	267.56	330.16	299.12	332.20	281.52	307.04	322.58	215.18	269.57
2009	317.97	253.09	285.91	330.19	276.15	303.39	293.10	205.25	249.98
2010	268.65	200.21	235.23	287.56	223.74	256.41	213.71	249.42	176.29
Total	299.13	234.06	267.13	311.61	259.44	285.97	288.37	212.19	250.91

^{Comparison between men and women. χ = 174.3, P < 0.001.}

^{Comparison between rural and urban areas. χ = 7174.3, P < 0.001.}

Data are expressed as the number of people with cancer per 100,000 people.

Cancer incidence

The incidence rate of all cancers in the registration areas ranged from 303.84/100,000 in 2006 to 268.65/100,000 in 2010 for men and from 243.01/100,000 to 200.21/100,000 for women (Table 1). Incidence was approximately 1.2 times higher in men than in women (Figure 1A). The incidence rate was 285.97/100,000 in urban areas and 250.91/100,000 in rural areas (Table 1). The rural: urban incidence ratio decreased from 0.89 in 2006 to 0.69 in 2010 (Figure 1B).

Figure 1

Relative Ratio of cancer burden in china by sex and districts. A. Male: female ratios for incidence and mortality. B. Rural: urban ratios for incidence and mortality. C. Male: female ratios for PYLL and DALY rates. D. Rural:urban ratios for PYLL and DALY rates. RR, relative ratio.

Cancer mortality

The average mortality rate for all cancers in 2006-2010 was 176.32/100,000; the rates for men and women were 220.54/100,000 and 130.60/100,000, respectively (Table 2). The male: female mortality ratio was 1.6 (Figure 1A). The cancer mortality rate in rural areas (179.25/100,000) was higher than that in urban areas (172.91/100,000) (P < 0.001), even though the incidence rate was lower in rural areas. The rural: urban ratio showed a tendency to decrease between 2006 (1.10) and 2010 (0.91).

PYLL and PYLL rates

In 2006-2010, the total PYLL owing to cancer was 95,737,626 person-years (Table 3). The number of years lost was greater for men (61,518,253, person-years) than for women (34,219,373 person-years) (P < 0.001). Although men have a lower life expectancy than do women (72.4 and 77.4 years, respectively), they lost more potential years of life than did women. PYLL rates were 16.45 and 11.22 for men and women, respectively (P < 0.001). The rate of premature cancer-related death was 1.46 times higher in men than in women in 2006-2010 (Figure 1C). Cancer patients in rural areas lost 1.4 times more person-years than those in urban areas in 2006-2010 (P < 0.001). The relative rural: urban ratio significantly decreased from 1.63 in 2006 to 1.22 in 2010.

DALY and DALY rates

Cancer caused an estimated loss of 131.44 million years of healthy life in 2006-2010 (86.20 million years for men and 45.23 million years for women) (Table 4). DALYs were greater for men than for women (P < 0.001). Patients in rural areas lost more years of healthy life (78.97 million years) than those in urban areas (52.46 million years) (P < 0.001). The DALY rate was 18.10. It was 1.6 times higher for men (22.19) than for women (13.87) in 2006-2010 (Figure 1A). The DALY rate was 1.3 times higher in rural areas (22.17) than in urban areas (17.09) in 2006-2010. The rural: urban ratio of DALY rates showed a tendency to decrease from 2006 (1.51) to 2010 (1.08).

Discussion

Cancer has been a major cause of mortality in China for many years [9-13]. Cancer burden studies provide information that guides health-related decisions, cancer control programs, and cancer treatment [24]. Our study shows that the incidence of cancer in China is lower than that in developed countries but higher than that in other developing countries [27]. The cancer mortality rate in China was higher than the worldwide rate and the rate in developing countries, but lower than the rate in developed countries [27]. According to a previous study, the worldwide average mortality rate for all tumor types was 112.10/100,000 in 2008 for both men and women, with crude rates of 124.0/100,000 and 99.0/10,000, respectively [25]. The mortality rate for individuals with malignant neoplasms was 223.1/100,000 (254.9/100,000 for men and 193.2/100,000 for women) in the developed world and 87.3/100,000 (96.1/100,000 for men and 78.2/100,000 for women) in the developing world [25]. Many global cancer studies had results similar to ours [28-31].

Factors responsible for the severe cancer burden in China include increased longevity, population aging, pollution, smoking, and unhealthy lifestyles [32-34]. Life expectancy in China has risen from 73 years (71 and 74 years for men and women, respectively) in 2005 to 74.8 years (72.4 and 77.4 years for men and women, respectively) in 2010 [9]. Aging is the main risk factor for cancer [35-37]. According to the China Population and Employment Statistics Yearbook 2007-2011, the percentage of elderly people (60 years of age and older) increased from 13.3% to 14.5%. Environmental pollution has also increased [14,20-22,38], and a previous study suggests that particulate matter with a diameter of 2.5 m (PM2.5) is the primary cause of lung cancer [39]. In China, the concentration of PM2.5 is rising owing to increased automobile exhaust, industrial pollution, and smoking in indoor establishments [40,41].

The PYLL and DALY indices were used to evaluate the severity of disease burden. PYLL is a quantitative indicator that assesses how cancer impairs public health based on the death toll and life expectancy [23,42]. DALY is a new comprehensive measurement of population health developed for the Global Burden of Disease study [6,43,44]. The loss of healthy life-years per 1000 people owing to malignant tumors is lower in China (18.10) than in developed countries such as Japan (48.27), South Korea (38.67), and Australia (38.03), but higher than in India (15.58) and the Arab nations (13.53) [45]. The number of cancer patients increases as the population ages [46]. Two-thirds of all cancers in China are associated with poor survival, which increases the cancer burden in this country [47].

Tumors were differentially distributed between urban and rural areas. Incidence was higher in urban areas, whereas mortality and PYLL and DALY rates were higher in rural areas in 2006-2010 in China. This may be explained by the greater exposure of urban residents to tumor risk factors such as air pollution. Urban residents are less physically active and have more social and mental pressures and more westernized lifestyles than rural residents, all of which may increase cancer incidence [48-51]. Higher mortality in rural areas may reflect limited medical care and poor economic levels [50]. Rural doctors in China are less educated and experienced than their urban counterparts, with a lower proportion of the former receiving formal medical education and training. Zeng et al. [47] found that rural areas often lack the medical resources required for prompt cancer diagnosis and treatment and that rural residents pay less attention to their health; as a result, cancers are detected at later stages, which increases mortality.

In our study, the rural: urban ratios for incidence, mortality, PYLL rate, and DALY rate all decreased from 2006 to 2010. The decrease in the rural: urban incidence ratio was statistically significant, suggesting that incidence will increase in urban areas. However, the rural: urban ratios for mortality, PYLL rate, and DALY rate decreased almost to 1, indicating that the cancer burden in rural and urban areas may become equal. This may reflect the trend toward urbanization and less healthy lifestyles (e.g., replacement of traditional foods with low-volume foods high in fat and low in fiber) [52]. However, further research is needed.

Tumor incidence, mortality rate, PYLL rates, and DALY rates ware all higher in men than in women in 2006-2010 in China. This may be explained by the unhealthy habits of men [53], such as smoking and drinking, and the more stressful lives of men. Because of their jobs, men may also have more exposure to carcinogenic factors than women [54].

In conclusion, the cancer burden in 2006-2010 in China was substantial, particularly for men and residents of rural areas. Early detection and early treatment of tumors should be a priority. Prompt, accurate screening of malignant tumors will help alleviate the tumor burden in China. Additional means of reducing the cancer burden include timely intervention in individuals at risk, comprehensive health education programs for Chinese residents, and development of effective strategies for preventing and controlling cancer. These steps should be implemented in China in the future.