Analysis of Relationships between Altitude and Distance from Volcano with Stomach Cancer Incidence Using a Geographic Information System.

Gastric cancer (GC) is the fifth most common cancer in the world, with a wide variation in incidence rates across different geographical areas. In Iran GC is the most common cancer in males and it is reported to be the third most prevalent after breast and colorectal in females. A geographical information system (GIS) allows investigation of the geographical distribution of diseases. The purpose of the present study was to explore the relationship between gastric cancer and effective climatic factors using GIS. The dispersion distribution and the relationship between environmental factors effective on cancer were measured using Arc GIS. Of all cases, 672 (73.8%) were in males with a sex ratio of 3 to 1. The highest incidence by cities was seen in Namin with 137.5 per 100,000. The results of this study showed that the distribution of GC around the Sabalan volcanic mountain was significantly higher than other places in the same province. These results can be considered as a window to future comprehensive research on gastric cancer.


Introduction
According to the estimations of the International Agency for Research on Cancer (IARC) in 2012, gastric cancer is the fifth most common cancer in the world (Kavousi et al., 2014), with a wide variation in incidence rates across different geographical areas. In Iran gastric cancer is the most common cancer in male and it is reported to be the third cancer after Breast and Colorectal cancers in female (Babaei et al., 2010). According to GLOBOCAN, gastric cancer in Iran accounted for 11.4% of all cases of cancer occurrence and the second most prevalent cancer and also most deadly cancer with 15.5 percent of all mortalities caused by cancers (Ferley et al., 2012). Ardabil is still one of the areas in the world that has the highest incidence of gastric cancer (Babaei et al., 2010;Sadjadi et al., 2003). Recently, the incidence and mortality rate of gastric cancer has dramatically fallen worldwide. In line with global reduction, the incidence rate of cancer has decreased in Asia as well. However, the incidence of gastric cancer in Iran remains very high at approximately 26.1 per 100, 000 (Rahman et al., 2014). In most countries there is a steady decline in the incidence and mortality from gastric cancer. However in the United States, like

Analysis of Relationships between Altitude and Distance from
Volcano with Stomach Cancer Incidence Using a Geographic Information System F Amani 1 , S Sadeghieh Ahari 2 , S Barzegari 3 *, B Hassanlouei 4 , M Sadrkabir 5 , Esmaeil Farzaneh 6 Iran, gastric cancer remains on the list of cancers that have a high mortality and is the reason for 2% of all deaths from cancer (Kasper et al., 2005).
Various risk factors for stomach cancer, such as smoking, nutrition and infection with Helicobacter pylori has been identified, but other factors such as geography and ethnicity also appears to be effective against the disease.
Despite the decline in the incidence of gastric cancer in the world but still in a developed country such as Japan and developing country such as Iran this rate is up and in fact, this reduction cannot be seen in some geographic areas.
On the other hand, the results of several studies have shown that the incidence of gastric cancer in volcanic regions, highland (such as Japan) is higher than other regions (Jesiis et al., 1995;Dogan et al., 2009;Javier et al., 2013;Junko et al., 2014). Ardabil and East Azerbaijan provinces have these features and the dormant volcano Mount Sabalan was located in Ardabil province and Sahand in East Azerbaijan province.
According to higher rate of mortality and gastric cancer incidence in two provinces, it seems that some geographic factors were effective in cancer incidence. So, the aim of this study was to investigate the relationship between the height and proximity to the volcanic mountains and the incidence of gastric cancer.

Materials and Methods
The study area Ardabil province is located at 37º9'21"-39º42'32" northern geographical latitude and 47º1'51"-48º54'7" eastern geographical longitude bordering south side of Aras River, east and south of eastern Azerbaijan and west part of gilan province and Azerbaijan Republic. Ardabil province has the 23th rank among 34 provinces of Iran considering human development. As it can be seen in map 1, this province encompasses 17, 800 km2 including 10 towns and 537 villages. According to census in 2012, Ardabil is a province with population of 1.248 million and population density of 70 per km2 (Statistical center of Iran, 2012). The majority of the population (more than 98%) is of Azeri ethnicity.

Study design and study population
This is a cross-sectional descriptive study and the statistical population included all registered gastric cancer patients in Ardabil about 1056 patients within March 2003 to September 2011. The participants were collected using documents and files available in cancer registry center (Aras) in Ardabil Imam Khomeini hospital. Because of non-exact location address in some patient's files, we used 910 patient's information in statistical analysis of data and GIS maps.

Data collection and analysis
From documents and records in the cancer registry in Imam Khomeini Hospital of Ardabil necessary information such as gender, occupation, age and place of residence and the exact address location were extracted. Collected data analyzed by statistical methods in SPSS.19 and also in Arc view GIS 10 for presentation the distribution of cancer cases.

Statistical analysis
We obtained the Latitude and longitude location of each patient by Google earth and then transferred to the Arc view GIS 10.1 software. The hot spot and Spatial autocorrelation (Moran's I) was done for distribution of patients and classified the patients in Buffers with 10 km from Sabalan Volcano in height 400 m. The incidence of gastric cancer in different height and distance classes according to the population and patients of each class calculated by GIS software. We used linear regression analysis with the software package SPSS.19 for investigation the relationship between height, distance from the volcano, and other factors with incidence of gastric cancer.

Results
Of all cases, 672(73.8%) were male and rest of them were female with sex ratio 3 to1. The incidence of gastric cancer by cities and residence place were in Table 1.
With replace cancer cases on Ardabil province elevation map ( Figure 1) and produce the height classes in 400 m, the results were in Table 2. Also created a buffer of 10 kilometers of volcanic mountains and add descriptive data on the map (Figure 2), the result of table 3 was obtained.
The results of hot spot and Spatial autocorrelation (Moran's I) analysis by Arc GIS software is presented in Figures 3 and 4.
The hot spot and Spatial autocorrelation (Moran's I) analysis can be observe the regular and irregular of diseases in one location and the effect of factors on diseases. The map produced by GiZScore. The irregular and cluster distribution of gastric cancer in areas of the province of Ardabil. To extract some hidden data on the map and to improve understanding of map hot spots, IDW interpolation was used. (Figure 5) The distribution of hot spots suggests that the closer to the volcano the people live the denser involvement with the cancer is observed. We used from linear regression method for study relationship between highest and GC Akan et al in a study showed that there was a significant relationship between cancer cases and environmental radioactivity. In this study, the higher GC incidence rate was seen in distance 50-70 km from Sabalan exactly around the Namin, Meshkinshahr and part of Ardabil which probably can be related to higher radiation of radioactive materials and volcanic soil type. The results show a high incidence of gastric cancer hypothesis in kilometers closer to Sabalan than longer distances can be  incidence. The results showed that there was a significant indirect relationship between distance to Sabalan with GC incidence, means that proximity to the volcano Sabalan increases the incidence of gastric cancer. It was found that the rate of GC in people from rural areas significantly higher than people from Urban areas. (Table 4)

Discussion
In this study according table 3, the mean incidence rate in distance 70 km from Sabalan with 70 per 100000 accepted (Akan et al., 2014).
In a study done in Chile about Urea nitrate and incidence rate of GC, results showed that despite the hypothesis that high nitrate due to stomach cancer, Nitrate concentration was higher in areas with a low risk of cancer which suggest the possibility of environmental cofactors involved in the conversion of nitrate to nitrosamine as a factor in gastric cancer. Also, in Chile study in the area with higher incidence rate the soil similar to soil of volcanic areas and contains high levels of Arsenic and low levels of selenium that could cause the conversion of nitrate to nitrous amines (Armijo et al., 1981).
Agustin et al in studies showed that more than 95% of countries with high level of digestive cancers, lymphoma, Leukemia and childhood cancers were in areas with radioactive materials and heavy metals such as copper, lead and cadmium (Amarel et al., 2006).
In our study, the rate of cancer in rural people was higher than urban people (64.3% v.s 35.7%) which weren't similar to other studies. These differences may represent the effect of other known or unknown environmental risk factors such as life style, agricultural poisoning and personal behaviors (Davoodabadi et al., 2003;Yazdanbod et al., 2007).
Of all cases, 73.8% were male and 26.2% were female and the sex ration 3 to 1 which was similar to other studies (Nourinayer et al., 2005;Yazdanbod et al., 2007). Also, in this study 42% of patients were farmer which was similar to other studies (Yazdanbod et al., 2007).
In our investigation 64.3% of patients were from rural, 80.9% Illiterate and 53.2% farmer and the rate of cancer incidence in low social economic levels were high which was similar to other study (Babaei et al., 2009;Ahari SS., 2013;Amorim et al., 2014).
The results of this study showed that the distribution of GC around the Sabalan volcanic mountain is significantly higher than other places in province, therefore, we can accept the hypothesis of increased incidence of gastric cancer in areas near the volcanic mountain. But the influence of other risk factors such as smoking and lifestyle should not be ignored.