Soc. SI:/. M,d. Vol. 23, No.3, pp. 241-247, 1986Printed in Great Britain

0277.9536/86 S3.00 + 0.00PCI'gamon Journals LId

GEOGRAPHICAL PA TrERNS OF CANCERMORTALITY IN CHINA

NINA SIU-NGAN LAMDepartment of Geography and Anthropology, Louisiana State University, llaton Rouge,

LA 70803, U.S.A.

Abstnct- This research note discusses the China cancer mortality data and the methc>dological problemsinvolved in spatial analysis of these data. Some of the research findings produced by mapping and analysesof the cancer data at the provincial level are also summarized. The two most common cancers in China,stomach and esophagus, were found to have no significant correlation with SOlT.le selected physicalvariables and population density, suggesting the need to examine other socio-economic variables such asdietary habit. The study also suggests that the type of diet which may be responsible for these two cancerscould be very different from each others. Colon and rectum, leukemia, and breast cal~cers were found tohave very high positive spatial autocorrelation and high correlation with population density-a resultcontrary to previous findings in the W'est. Future research using a geographic information systemapproach and county data is suggested.

Key words-china, cancer mortality. geographic information systems, computer mapping, spatialautocorrelation, factor analysis

,..,

INTRODUcnON

The study of geographical variations in cancer mor-tality has often been regarded as an effective meansof deriving etiologic hypothesis [1]. Numerous studieson the geographical patterns of cancer mortality inthe United States and other parts of the world havebeen made (see for examples [2] and [3]). The geo:graphical pattern of cancer mortality in China, how-ever, has not yet been systematically studied, partlybecause of the unavailability of data in the past. Thisis unfortunate since China has almost a quarter of theworld's population and has a wide variety of environ-ments. Studies on the geographical variations ofcancers in China can provide a better understandingof how these cancers affect China and could alsoenhance comparisons among different countries withparticular reference to the search for the causes ofcancers.

The recent publication of an atlas of cancer mor-tality in China, based on data collected in 1973-75,emphasizes the importance of such geographical vari-ations [4]. In the atlas, the sex-specific rates of thenine most common cancers by xi an (i.e. county) aregeneralized and shown in the fonn of choroplethmaps. In addition, the original sex-specific mortalityrates by provinces are listed as tables. (There are 2392counties in mainland China, belonging to 29 prov-inces. autonomous regions and municipalities; Fig.1.) These mortality rates are age-adjusted to the 1964census population of China, the 1960 world standardpopulation, and the 1960 world standard populationbetween 35 and 64 years old. This is perhaps theearliest set of data in China that has been system-atically collected and recorded at the county level.

Many researchers believe that most cancers arccaused by environmental factors and are thereforetheoretically preventable once the causal factors havebeen identified [5]. It will be useful to study the case

24\

of China so that preventive measures could be madepromptly during China's rapid pace of mod-ernization. Since the cancer data at the county levelare not yet available outsid,c China, a geographicalstudy based on the provincial data is made. In thisstudy, the nine most common cancers in China,which lead to a total of 16 sex-specific sites, weremapped by computer. Spatial autocorrelation analy-sis and factor analysis were applied to examine thecancer map patterns and their relationships withenvironmental factors. The findings from this studymay not be further generalized simply because thestudy was based on provincial data. Conclusive state-ments about cancer patterns in China must awaitdata of a finer resolution (i.e. by county). The objec-tive of this study is to illustrate the geographicalpatterns at the provincial scale [6, 7], which serves asa useful supplement to future studies of this regionusing more detailed data.

The purposes of the present research note are:(1) to outline the data and to discuss some meth-odological problems involved in studying China'scancer mortality patterns; (2) to highlight some ofthe interesting findings from the study, focusing onthe two most common cancers, stomach and esopha-gus, in China; and finally (3) to identify possibleresearch directions in the China case.

ME11fODOLOGICAL PROBLEMS

In studying the geographical patterns of diseasemortality, at least six methodological problemsshould be considered [1,7]. First, the mortality rateused does not necessarily reflect the rates of occur-rence because some cancers are more likely to lead tomortality than others. Second, the place of death maybe different from the place of residence where thedisease was acquired. This is particularly the case

..Fig. I. Provinces. municipalities and autonomous regions of China.

graphical variations of cancers using more detaileddata for a large region is often a major task of dataprocessing, analysis, and mapping. This is perhapswhy studies using more detailed data for a largeregion have rarely been made. The problem is furthercomplicated by the fact that attempts are often madeto correlate cancer data with other types of data (e.g.census, soil type, vegetation cover), but these varioussets of data may not be based on the same areal units[8,9]. Recent developments in geographic informa-tion systems which permit the use of more detaileddata could contribute to the study of the geographicalvariations of cancers as well as to health preventionin general [10].

where migration occurs frequently. However, itshould be noted that migration is fairly restricted inChina. Therefore, if environmental factors do play animportant role in causing cancers, they should bedetected more easily in China than in other countriessuch as the United States where migration is frequentamong the population. Third, the findings from dataof one scale may be different from those of anotherscale. Therefore, we should interpret the findings withdue consideration to the effect of :;cale in order toavoid the ecological fallacy. On the other hand, scalemay also help to determine the nature of moreintensive studies in the future.

Fourth, high mortality does not nc:cessarily suggestprevalence of certain environmental factors but maybe a result of lack of preventive health measures. Thisproblem has seldom been mentioned, but it may bea significant aspect particularly in developing coun-tries. Fifth, correlations found between environ-mental factors and cancer sites do not necessarilyimply causation. The results of this type of study maybe suggestive but they can rarely be definitive. Lastbut not least, a comprehensive analysis of the geo-

CANCER MORTALITY PAlTERNS INCHINA-50ME HIGHLIGHTS

The data collected for the period 1973-75 revealthat the total number of deaths due to cancer is about700,000 per year, or about II % of the annual totalmortality. The national average age-adjusted cancermortality rate is 80.17 per 100,000 for male, and 54.27

Geographical patterns of cancer mortality in China 243

Table I. Rank-order of the 16 most common sex-specific cancers

National rateRank Cancer site (deaths/I 00.000)'

I23456789

10II

1213141516

20.9310.1619.689.85

14.525.619.986.823.204.083.032.792.232.612.491.27

for male and the third for female. Furthermore,cancer severely affects the young and working popu-lation. It was the leading cause of death for the agegroup of 35-74, and the second leading cause ofdeath for the age group of 15-34.

The nine most common cancers in China are, indecreasing order of magnitude, stomach, esophagus,liver, cervix uteri, lung, colon and rectum, leukemia,breast, and nasopharynx. Table I lists the sex-specificrates of these nine most common cancers. It showsthat for the same cancer female always has lowermortality than male. With regard to the spatialpatterns, both the maps at the provincial scale and atthe county scale show the existence of large spatialvariations within and among various cancers,whereas the spatial patterns between male and femalefor the same cancer are generally very similar. This isalso reflected by the spatial autocorrelation analysisand the factor analysis using provincial data, inwhich male and female for the same site were foundto have similar spatial autocorrelation statistics andgenerally belong to the same factor.

Stomach-MStomach-FEsophagUJ-MEsophagUJ-FLiver-MLiver-FCervix uteriLung-MLung-FColon and =tum-MColon and =tum-FLeukemia-MLeukemia-FBfQSt-F

Nasopharynx-MNasopharynx-F

.Age-adjusted to the 1964 census population of China.

per 100.000 for female. On average. one person willdie of cancer every 45 sec in China. During the1973-75 period. can~f was the second cause of death

..

NINA Slu-NoAN LAM244

,.Fig. 3. Mortality map of stomach cancer for female, by province. municipality and autonomous region.

Age-adjusted to 1964 census population of China.

gested that stomach cancer was associated with indi-ces of poor social conditions [11], rural and semi-rural areas [12], poor drinking water quality [13] andspecial dietary and ethnic background [14, 15]. On theother hand, conflicting reports on the relationshipsbetween stomach cancer and the rate of primaryindustry in Japan have also been made [2]. Based onthe map patterns shown here, it is expected thatstomach cancer in China is generally related to thedietary and ethnic background, and the level ofeconomic development.

Esophagus cancer, the second highest cancerdeaths in China, has a very different spatial patternfrom stomach cancer. Areas of high stomach mor-tality generally coincide with low esophagus mor-tality, and vice versa. Both male and female esopha-gus cancers show high rates clustering in thenorth-central and eastern parts of China (Figs 4 and5). An exception is Jiangsu Province where mortalityrates for both cancers are high. Esophagus cancer isless common in the United States, Canada andEngland but more common in central Asia. Previous

When the mortality rates are mapped at the pro-vincial scale, the spatial patterns of some of thecancer sites can be detected and compared moreeasily. The patterns of the two most common cancers,stomach and esophagus, are used as examples here.For stomach cancer, China's leading form of cancerdeaths, both male and female have high rates in thewest and north-west, including Xizang, Qinghai,Ningxia and Gansu (Figs 2 and 3). These provincesare characterized by a cool and dry climate, lowpopulation density, high concentration of minoritygroups, and a low level of economic development.However, the Jiangsu Province on the east coast witha warm and wet climate. high population Ijensity, lowconcentration of minority groups, and a high level ofeconomic development also has high stomach mor-tality rates for male and female.

In comparison. Japan. Chile and the northernEuropean countries have high rates of stomach can-cer. In the United States. Canada. England, Australiaand New Zealand, stomach cancer mortality is stillhigh but has been declining. Previous studies sug-

Geographical patterns of cancer mortality in China 245

ated with different factors. Pearson correlationcoefficients between the factor scores of these twofactors and some selected variables were calculated.These variables include: population density in 1973[18,19], elevation, temperature, rainfall, latitude andlongitude [20,21]. No significant correlation wasfound between these two factors and the selectedvariables, indicating the need to examine other vari-ables in the future, particularly those related tosocio-economic condition and dietary habit.

Another interesting finding from this study relatesto colon and rectum, leukemia and breast cancers.These cancers exhibit a random pattern at the countylevel, but when the data are aggregated at the pro-vincial level, the patterns become highly concen-trated. In the cases of colon and rectum cancer andleukemia for both sexes, high rates occur along theeast coast, especially in Jiangsu, Zhejiang, Fujian andShanghai. These provinces are generally more popu-lated and urbanized. Highest rates of breast canceroccur in the three municipalities of Beijing, Tianjinand Shanghai, and their surrounding areas. It is

studies indicated a strong association between thiscancer and dietary habits as well as hygiene condition[16,17]. However, based on the map patterns shownhere, it is suspected that the dietary habits could bevery different from those associated with stomachcancer. It is also noted that the southern part ofChina has very low mortality rates in both stomachand esophagus cancers. This region is characterizedby a wann and wet climate, and the dietary habit inthis region is also quite different from the north-central and western part of China. For example,pickled vegetables, which were found to be related toesophagus cancer, are much more common in the dietof the north and central part of China than in thesouth [16]. On the other hand, salted fish, a commondiet in the south (especially in the Guangdong Prov-ince), was found to be related to nasopharyngealcancer.

The difference in the spatial patterns betweenstomach and esophagus cancers is also highlighted byfactor analysis. Factor analysis of the 16 sex-specificcancer sites reveals th.a~ these two cancers are associ-

.

Fig. 4. Mortality map of esophagus cancer for male, by province. municipality and autonomous region.Age-adjusted to 1964 census population of China.

246 NINA Slu.NGAN LAM

.Fig. 5. Mortality map of esophagus cancer for female. by province. municipality and autonomous region.

Age-adjusted to 1964 census population of China.

notable that colon and rectum and breast I:ancers arealso the predominant causes of cancer deaths inhighly developed countries such as United States,Canada and England, but these two cancers are lesscommon in China. Based on their map patterns, it isexpected that these cancers are related to factorsgenerated from areas of intensive urbanization andpopulation density. These factors may include, forexample, high degrees of air, water and noise pollu-tion produced by intensive automobile use, and ahigh density of factories and population.

The factor analysis shows that colon and rectum,leukemia and breast cancers for both male andfemale, together with male and female lung cancers,form a distinct group and score high on factor I.Factor I was found to be highly correlated withpopulation density, a result of urbanization andindustrialization. Factor I was also found to besignificantly related to elevation and longitude.These relationships seem to be indirect because lowerelevation is likely to attract more people and the eastcoast of China has all the major urban centers.

The highly clustered patterns of the above cancersare also reflected by the high positive spatial auto-correlation statistics calculated from their patterns.This is quite different from Glick's study of the cancerpatterns in Pennsylvania [6] where leukemia andbreast cancers were found to have very low andinsignificant autocorrelation at the county level. It isnot clear at this stage whether such difference is solelydue to differences in scale or a result of environmentaldifferences between these two places.

FUTURE RESEARCH

This research note focuses attention on the meth-odological problems involved in spatial analysis ofcancer data in general and with special referenceto China. It also highlights some of the findingsproduced by mapping and examining the cancermortality rates at the provincial level. Some of thefindings agree with results from other regions (e.g.those related to stomach and esophagus cancers), but

Geographical patterns of cancer mortality in China 247

some do not (e.g. those related to colon and rectum.leukemia and breast cancers).

This study also points to the need for data at thecounty level in order to thoroughly examine thespatial patterns of cancer mortality and to accuratelyidentify the environmental factors. This means amajor task of data collection because both the age-and sex-specific rates and a set of physical andsocio-economic variables will be required. Such de.tailed studies involving voluminous data (about 2392counties) could be made more efficiently by using ageographic information system approach. Researchalong these lines is being conducted by the author.

Acknowledgement -This research is partially supported bya grant from the Association of American Geographers.

8. Goodchild M. F. and Lam N. SoN. Areal interpolation:a variant of the traditional spatial problem. Geo-processing I, 297, 1980.

9. Lam N. SoN. Spatial interpolation methods: a review.Am. Cartograph. 10, 129. 1983.

10. Pyle G. F. Applied Medical Geography. Chap. 8. Wiley,New York, 1979.

II. Stocks P. Regional and Local Differences in CancerDeath Rates. General Register Office. Studies on Medi-cal and Population Subjects, No. I, London. HMSO.n.d.

12. Statistics Canada. Mortality Atlas of Canada, Vol. I:Cancer. Canadian Government Publishing Center. Hull.Quebec, 1980.

13. McGlashan N. D. European male stomach cancer inSouth Africa: a cartographic appraisal. In MedicalGeography (Edited by McGlashan N. D.). pp. 187-198.Methuen, London. 1972.

14. Chaikin A. V. The geographical distribution of cancerin the Soviet Union. SOI1. Geograph. 3, 59. 1962.

15. Mason T. J., Mackay F. W.. Hoover R.. Blot W. J. andFraumeni J. F. Jr. Atlas of Cancer Mortality for u.s.counties 195a-/969. U.S. Government Printing Office,Washington, D.C., 1975.

16. WGBH/BBC. The cancer detection of Lin Xian. Nol1aSeries, 1981.

17. McGlashan N. D. Food contaminants and oesophagealcancer. In Medical Geography (Edited by McGlashanN. D.), pp. 247-257. Methuen. London. 1972.

18. Pannell C. W. and Ma L. J. C. China-The Geographyof Development and Modernization, p. III. HalstedPress. New York, 1983.

19. Tai Kung Pao (Tai Kung Newspaper), Hong Kong.October 30. 1982.

20. Wu J. Y. (Ed.) The Vegetation of China, pp. 33-120.Science Press, Beijing. 1980.

21. Central Meteorological Office. The Climatic Atlas ofChina. China Map Press. Beijing, 1978.

REFERENCES

I. Mayer J. D. The role of spatial analysis and geographicdata in the detection of disease causation. Soc. Sci. M~d.17, 1213. 1983.

2. Inaba Y.. Yanai H.. Takagi H. and Yamamoto S. Astudy of the geographical patterns of cancer mortalityfor selected sites by means of factor analysis. Soc. Sci.M~d. ISO, 233. 1981.

3. Babin E. United States cancer mortality regions:19S0-fJ9. Soc. Sci. M~d. 130, 39, 1979.

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S. Glick B. J. The spatial organization of cancer mortality.AM. Ass. Am. G~ogr. 71, 471. 1982.

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