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Disparity and trends in the incidence and mortality of lung c ancer in the world

1Department of Epidemiology and Biostatistics, School of Public Health, Isfahan University of Medical Sciences, Isfahan, Iran 2Zabol University of Medical Sciences, Zabol, Iran 3Gonabad University of Medical Sciences, Gonabad, Iran 4Department of Social Medicine, School of Public Health, Dezful University of Medical Sciences, Dezful, Iran 5PhD Candidate, Social Determinants of Health Research Center, University of Social Welfare and Rehabilitation Sciences, Tehran, Iran 6Department of Epidemiology and Biostatistics, School of Public Health, Shahrekord University of Medical Sciences, Shahrekord, Iran 7Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran

and regularly monitored in developed countries [13][14][15][16] however, there are not enough numbers of studies on the disparity in the distribution of incidence and mortality of this cancer based on different geographical or Socio-Economic indexes for areas at the national and international level [17]. Therefore, there are not identified geographical disparities caused by this disease at the global level. The aim of this study was to investigate the geographical distribution of LC incidence and mortality based on the development level, WHO classification, human development index levels and the world's continents in 2012, as well as the trend of incidence and mortality of LC during 1975 to 2010 based on the gender in the worldwide.

Methods
In the present study, we extracted the information on the incidence and mortality of LC in 184 countries from the International Agency for Research on Cancer (IARC) (Project GLOBOCAN, 2012). GLOBOCAN is a database on various types of cancers and it is created by the World Health Organization. It covers information on the number, raw rates, and age standardization of cancer incidence, prevalence and mortality for different regions and countries. Currently, the available data in GLOBOCAN is known as one of the newest international database on the cancer. Based on the data of GLOBOCAN project, it is possible to investigate and compare the incidence and mortality of cancer based on the type of cancer, age and gender groups for different regions of the world.
The present study categorized and presented the information on the Age-Standardized Incidence Rate (ASIR) and Age Standardized Mortality Rate (ASMR) of LC based on the continents (Africa, Latin America and Caribbean, Northern America, Europe, Oceania, Asia), world regions based on the development level (More developed regions and Less developed regions) and human development index (very high, high, medium, or low).
We provided the information about the incidence and mortality of LC based on the number, raw rates and the Age-Standardized rates in 2012. We also expressed raw and standardized rates of incidence and mortality per 100,000 people. Geographical Distribution Map was prepared for the ASIR and ASMR of this disease based on the age-specific rates. Detailed descriptions of applied methods are presented in previous reports [18][19][20][21].

(a) The ASIR and ASMR of LC in the world
In 2012, 1824701 new cases of LC were diagnosed worldwide. From this number, 1241601 (68.04%) cases occurred in men and 583100 (31.96%) in women. In general, the ASIR of LC was equal to 23.1 (34.2 in men and 13.6 in women). The sex ratio (male to female) of the newly diagnosed LC was equal to 2.13 (Figure 1).
There were also 1589925 deaths from LC during this year. From this number, 1098702 (69.1%) cases occurred in men and 491223 (30.9%) in women. In general, the ASMR of LC was equal to 19.7 (30 were in men and 11.1 in women). The sex ratio of the mortality of LC was equal to 2.24 ( Figure 2).

(b) The ASIR and ASMR of LC based on the continents
The ASIR of LC was equal to 38.3 (44 in men, and 33.8 in women) in North America, 29 (46.2 in men, and 15.1 in women) in Europe, 25.3 (31.3 in men and 20 in women) in Oceania, 23.4 (35.2 in men and 12.7 in women) in Asia, 13.7 (18.7 in men and 9.6 in women) in Latin America, and 5 (7.7 in men and 2.6 in women) in Africa. From the total number of this disease in the world, the highest proportion occurred in Asia and the lowest proportion in Oceania, so that 57.3% of cases occurred in Asia, 22.5% in Europe, 13.2% in North America, 4.7% in Latin America, 1.6% in Africa and 0.7% in Oceania (Table 1 and Figures 1, 2 and 3).

(d) The ASIR and ASMR of LC according to the WHO classification
The ASIR of LC was equal to 32.8 (48.9   in regions with very high HDI, 12.1% in regions with high HDI, and 2.2% in regions with low HDI ( Table 1). The ASMR of LC was equal to 23.9 (34.1 in men, and 15.6 in women) in regions with very high HDI, 16.4 (28.6 in men, and 6.9 in women) in regions with high HDI, 21.6 (32.6 in men and 11.7 in women) in regions with medium HDI, and 4.8 (7.1 in men and 2.8 in women) in regions with low HDI. From the total mortality of this disease, 49.1% occurred in regions with medium HDI, 36.4% in regions with very high HDI, 12.3% in regions with high HDI, and 2.2% in regions with low HDI ( Table 2).

(f) The trend of LC ASIR and ASMR during 1950 to 2010
The total trend of ASIR and ASMR of LC was descending in men during 1975 to 2010, while it was quite different in women and it was ascending during this period. Figures 4, 5, 6 and 7show the trend of incidence and mortality of LC in men and women in some countries during 1975 to 2010.

Discussion
The present study aimed to investigate the distribution of LC incidence and mortality worldwide based on the WHO classification, the world's continents, development level, and the HDI level based on the gender in 2012. It also studied the trend of incidence and mortality of LC based on the gender for some selected countries during 1975 to 2010. In 2012, there were 1824701 new cases of LC in worldwide, of which 68.04% were in men and 31.96% in women. This year also had 1589925 deaths from this disease of which 69.1% were in men and 30.9% in women. The highest ASIR and ASMR of LC occurred in North America, more developed regions, and the WPRO region of the WHO, and regions with very high HDI. Furthermore, the lowest ASIR and ASMR of LC occurred in Africa, the less developed regions, the AFRO region, and regions with low HDI. The ASIR and ASMR of LC was descending in men, but ascending in women in most of the world's countries from 1975 to 2010.
The highest ASIR and ASMR of LC occurred in areas with very high HDI, but the lowest rate was seen in areas with low HDI. Similar results with the present research were found in a study by Pakzad et al on the relationship between the HDI and the ASIR and ASMR of LC in Asian countries. According to their study, an increase in the HDI led to the increased ASIR and ASMR of LC, so that the correlation was equal to 0.345 between the HDI and the ASIR, and equal to 0.289 with ASMR, that it was statistically significant [17]. High life expectancy and average life span were the main reasons for the high ASIR and ASMR of LC in regions with very high HDI. These regions may also have much higher prevalence of smoking than other regions of the world. For instance, the annual cigarette consumption per capita was increased more than 70 times (from 54 to 4,000 cigarettes) in the United States from 1880 to 1970 (12). On the other hand, there might be the under estimate of incidence and mortality number of cancer cases in regions with low HDI due to the existing problems with diagnosis of the disease as well as problems with the registration of cancer cases, and thus the actual cases of this disease were higher than the diagnosed and recorded cases. These problems have also been observed in other cancer studies [19,20,[22][23][24][25][26][27][28].
In this study, the incidence and mortality number of LC in men was twice as high as in women, so that 68% of incidence and 69% of mortality of LC occurred in men. Similar results were observed in a study by Pakzad et al in Asian countries, to that 71.13% of new cases and 71.45% of deaths occurred in men in Asia during 2012 [17]. Probably, the main reason for the disparity in the incidence and mortality of LC among men and women is the disparity in their exposure to the risk factors of the disease.
The geographical distribution of LC was largely associated with the prevalence of cigarette smoking, so that in Kentucky State of the United States, where the prevalence of cigarette smoking was equal to 30%, the ASIR of LC was 125.9 in men, and 80.3 in women per 100,000 people, while in California, where the prevalence of cigarette smoking was 14%, the ASIR of LC was 60.4 in men and 44.4% in women per 100,000 people [29]. During 1973 to 2007, the incidence of LC was steadily decreasing in white women in California, while no decreasing trend of mortality was seen in women in Midwestern and Southern States, indicating the effectiveness of control programs in reducing the incidence of cigarette smoking in California State [30].
The maximum prevalence of cigarette smoking in men has been two decades earlier than women; hence, it is expected that the epidemic of this LC will begin in women at a time interval after men. The incidence of LC in men has been descending over the past few decades, while the incidence of this disease is still ascending in women [30]. Despite the fact that the number of men, who annually die from LC, is much higher than women, it is expected that over the years to come the disparity in mortality rates between both genders will become minimal [10].
Cigarette is thus one of the most important factors affecting the incidence of LC worldwide. Furthermore, due to the high cost and limited effectiveness of screening methods and therapeutic measures in LC, cigarette is one of the key factors in the death from LC [31]. Therefore, effective measures can be taken to reduce the incidence of cigarette smoking to reduce the burden of LC in the global arena especially in the African regions and some Asian countries with limited access to screening and treatment programs [32]. In areas such as Australia, California and Hong Kong, which have begun the cigarette prevention programs, the incidence of LC is expected to reduce significantly especially in men. Since there is a long latency interval between smoking and occurrence of LC, the incidence of LC will significantly increase in countries like China, where there is not any adequate program to reduce the prevalence of cigarette smoking, in the upcoming decades [33]. Therefore, governments should adopt appropriate planning and policies to prevent LC. In addition to reduction of the prevalence of smoking, they should also reduce the exposure to other well-known risk factors such as Asbestos, Radon, air pollution, occupational carcinogens and second-hand smoke [34,35].

Study Limitations
This study, has been conducted using data of GLOBOCAN project of World Health Organization(WHO) in 2012. The aim of the GLOBOCAN project is to provide contemporary estimates of the incidence, mortality and prevalence from major types of cancer, at national level, for 184 countries of the world. Although data from the GLOBOCAN project is currently the most comprehensive source of information on the distribution of cancers worldwide. Nevertheless, one of the limitations of this study is the use of data of 2012, due to the lack of newer data in the global level. Also, the quality of collected cancer data in the GLOBOCAN project is not similar in all countries especially those with medium or low HDI, so that the estimates of some countries are based on the recorded cases of cancer in limited areas or based on estimates from neighboring countries [36].

Conclusions
The highest ASIR and ASMR of LC occurred in North America, more developed regions, and the WPRO region of the WHO, and those regions with very high HDI. Furthermore, the lowest ASIR and ASMR of LC occurred in Africa, the less developed regions, the AFRO region, and regions with low human development indexes. Most regions of the world had decreasing incidence and mortality of LC in men and increasing trend in women.

Open Access
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