|BREAST CANCER SYMPOSIUM: ORIGINAL ARTICLE
|Year : 2014 | Volume
| Issue : 3 | Page : 277-281
Rural urban differences in breast cancer in India
RT Nagrani1, A Budukh1, S Koyande2, NS Panse3, SS Mhatre1, R Badwe4
1 Department of Epidemiology, Centre for Cancer Epidemiology, Tata Memorial Centre, Mumbai, India
2 Mumbai Cancer Registry, Indian Cancer Society, Mumbai, India
3 Barshi Rural Cancer Registry, Nargis Dutt Memorial Cancer Hospital, Barshi, District Solapur, Maharashtra, India
4 Department of Surgical Oncology, Tata Memorial Hospital, Mumbai, India
|Date of Web Publication||10-Dec-2014|
R T Nagrani
Department of Epidemiology, Centre for Cancer Epidemiology, Tata Memorial Centre, Mumbai
Source of Support: None, Conflict of Interest: None
Context: Breast cancer incidence rates are high in developed countries and much lower in less developed countries including India. Aims: The aim of the following study is to compare breast cancer incidence rates in rural, urban and metro regions of India and to estimate risk of developing breast cancer associated with residence in a rural area. Settings and Design: Descriptive and analytical study design. Materials and Methods: We extracted age adjusted incidence rate from 26 population-based cancer registries and data from hospital-based case-control study to estimate rate and risk ratio for developing breast cancer in an urban region compared with a rural residence. Statistical Analysis: The rate ratios and 95% confidence interval (CI) for developing breast cancer in the urban and metro region compared with rural registry of Barshi were estimated. The odds ratio (OR) and 95% CI for developing breast cancer in women residing in a rural region was estimated by fitting unconditional logistic regression using hospital-based case-control study data. Average annual percentage change in most recent 15 years (1996-2010) for Barshi (rural), Aurangabad (urban), and Mumbai (metro) cancer registry was obtained by fitting a log-linear model using joint point regression. Results: Living first 20 years of life in a rural area reduces the risk of breast cancer (OR = 0.65, 95% CI: 0.56-0.76). Conclusions: The current study demonstrates that lifestyle operative in a rural area is protective against risk of developing breast cancer.
Keywords: Breast cancer, cancer registry, rural, urban
|How to cite this article:|
Nagrani R T, Budukh A, Koyande S, Panse N S, Mhatre S S, Badwe R. Rural urban differences in breast cancer in India
. Indian J Cancer 2014;51:277-81
| » Introduction|| |
In 2012, 1.7 million women globally were diagnosed with breast cancer and there were 6.3 million women alive who had been diagnosed with breast cancer in previous 5 years.  In countries with high and medium human development index (HDI) an increase in female breast cancer has been observed. 
Within India, there are substantial differences in the incidence rates of breast cancer in rural and urban areas: This indicates that the transition from rural to an urban society is associated with an increase in breast cancer risk. The cause of this strong rural urban difference in breast cancer incidence is not known although it is likely to be due to one or more westernized lifestyle which differs strongly between rural and urban women.
In order to better gauge and interpret the difference in breast cancer incidence by residential status, we compared rates in rural, urban and metro regions. We also studied the secular trends in incidence rates from 1996 to 2010 in selected rural, urban and metro registries of India. Finally, we have utilized hospital-based case-control data to emphasize the differences in risk of developing breast cancer according to residence in rural and urban regions. 
| » Materials and Methods|| |
We obtained the incidence data on invasive breast cancer cases in females from 26 population-based cancer registries across India published by National Cancer Registry Program (NCRP) namely Ahmedabad Rural, Aizawl District, Aurangabad, Bangalore, Barshi, Bhopal, Cachar District, Chennai, Dibrugarh District, East Khasi District, Imphal West District, Kamrup Urban District, Manipur, Meghalaya, Mizoram, Manipur excluding Imphal West, Mumbai, Mizoram excluding Aizawl, Nagaland, Nagpur, New Delhi, Pune, Sikkim, Thiruvananthapuram, Tripura, and Wardha. The population-based cancer registries collect data on all cancer cases residing in the respective registry area for the duration of >1 year. Information is collected on demographic details, the method of diagnosis, date of diagnosis, site of the tumor, histology and treatment. The details of practices at the cancer registry are described in the NCRP report. 
Definition of rural and urban regions
To better understand the impact of risk factors on the breast cancer burden and to aid future planning, we divided the population-based cancer registries across India into rural, urban and metro regions and further stratified by menopausal status to estimate the difference in the incidence rate of female breast cancer cases.
Depending on the definitions from census of India, 2001 the registries were classified into metros (population >1,000,000); urban (population between 25,000 and 1,000,000). The registries were classified as rural depending on the definition used by the registries and census of India, 2001 (population <5000). , However, registries in north eastern regions include cases from the entire state or from the entire district, i.e. the registry area includes both rural and urban regions; therefore they have been grouped separately. Breast cancer incident cases (International Classification of Diseases [(ICD-10) C50]) were extracted from Barshi, Mumbai, and Aurangabad on restricting the analysis from 1996 through 2010 and to the ages 25-74, in order to examine recent trends according to residential status over the 15-year period. Corresponding population-at-risk were obtained from census information. 
For defining residential status in an ongoing hospital-based case-control study; information of residential history was obtained from female study participants (1637 breast cancer cases and 1515 visitor controls). The residential history has information of all the study participants living for 1 year or more at a given residence from age zero to their completed the age at the time of enrolment. The rural and urban residence status was self-reported by study participant. Study participants were stratified into rural and urban using four different definitions as follows:
- Ever lived in a rural area: If a study participant has ever lived in a rural area (self-reported) for 1 year or more in life is termed as a "rural participant", whereas any participant who has never lived in a rural area is termed as "urban participant"
- First 20 years lived in a rural area: If a study participant has lived first 20 years of her life in a rural area, i.e. from age 0 to age 20, then participant is classified as "rural participant," whereas any participant who has lived <20 years in a rural area is classified as "urban participant"
- Currently living in a rural area: Any study participant who has a current residence (at the time of enrolment) of 1 year or more in a rural area is termed as "rural participant", versus a current residence in an urban area is an "urban participant"
- Total years lived in a rural area:
- 1-10 years: A minimum of 1 year and a maximum of 10 years lived in a rural area versus never lived in a rural area are categorized as rural and urban participants respectively
- >10 years: If total years lived in a rural area is >10 years, study participant is categorized as rural or else urban.
We extracted age-standardized (world standard) incidence rates per 100,000 women years for 26 different population-based cancer registries included in NCRP.  The rate ratios (RRs) for different registries were estimated using Brashi rural registry as reference.  We grouped the incidence data into 25-44 years (pre-menopausal) and 45-74 years (post-menopausal) assuming median age of attaining menopause is 45 years. The average annual percentage change in most recent 15 years (1996-2010) was obtained by fitting a log-linear model using joint point regression. 
The OR for developing breast cancer in urban areas compared to a rural region and their 95% CI for four definitions of residential status were estimated through unconditional logistic regression models. The ORs were adjusted for age and for the region of residence (whether living in north, south, east, west or central India). Analysis was performed using the statistical package Stata SE 12 (StataCorp LP, College Station, TX). 
| » Results|| |
The RR of Ahmedabad rural registry was 0.90 while that for urban and metro registries were in the range of 1.48-2.23 and 1.89-2.98, respectively compared to Barshi rural registry. The RR for north eastern registries varied widely between 0.58 in Tripura to 2.47 in Aizawl District compared with Barshi rural registry [Table 1].
|Table 1: Incidence rate and rate ratio of developing breast cancer in selected cancer registries stratified by rural, urban, and metro regions |
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As shown in [Table 2], ratios of post-menopausal to pre-menopausal women were 8.92 and 8.48 in rural registries of Barshi and Ahmedabad respectively whereas in urban registries such as Aurangabad, Bhopal and Wardha the RRs were 8.90, 10.75, and 6.82, respectively. However, the post-menopausal to pre-menopausal ratios in registries located in metros of India were much higher (except Nagpur) compared to that in rural and urban regions.
Statistically significant trend of breast cancer incidence in Mumbai cancer registry (metro region) was observed (1.6 [1.0-2.2]) in last 15 years period (1996-2010). Similar increase, but not reaching statistical significance was observed in rural (Barshi) and urban (Aurangabad) registries [Table 3].
|Table 2: Breast cancer incidence rates in premenopausal and postmenopausal women for selected cancer registries stratified by rural, urban, and metro regions of India |
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|Table 3: Trend of breast cancer in rural, urban, and metro regions of India. Year: 1996-2010 |
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[Table 4] shows that ever lived in a rural area provide protection from breast cancer when compared to participants who never lived in a rural area. A protective association was observed in women living >10 years in a rural area (odds ratio [OR] = 0.81 [0.70-0.93]). An OR of 0.90 with 95% confidence interval 0.83-0.96 was observed with per year lived in a rural area. Moreover, the first 20 years of a life spent in a rural area was observed to provide protection from breast cancer compared to those who lived <20 years of life in rural areas.
|Table 4: Residence in rural area and risk of developing breast cancer: Estimates from case-control study in Mumbai. Year: 2009-2013 |
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| » Discussion|| |
The results of the present study are derived from data collected in 26 different cancer registries in India, having a reasonably reliable and complete data.  The data of some of the registries (Bangalore, Barshi, Bhopal, Chennai, Mizoram, Mumbai, New Delhi, Pune, Sikkim, Thiruvananthapuram) have also met the criteria for inclusion in a recent volume of cancer incidence in five continents series published by the International Agency for Research on Cancer.  In this study, we have conducted a detailed analysis to understand the cause and estimate the difference in the incidence of breast cancer cases in women living in rural and urban areas and to identify the trend of breast cancer in rural and urban India in last 15 years (1996-2010).
An increasing order of RRs was observed in the present study from rural to urban to metro regions, clearly suggesting the underlying differences in the incidence rates between rural and urban regions. Similarly, in the case-control study we observed a "dose-response" relationship between numbers of years lived in rural areas and increase in protection from breast cancer development indicating that women living for many years in rural areas adhere to lifestyles, which are protective against breast cancer. A current residence in a rural area compared to current residence in an urban area does not give protection against breast cancer. However, protection was observed (not statistically significant) in women currently living in rural areas compared to women who have never lived in a rural area. Furthermore, residence in first 20 years of life in rural areas was observed to be a protective factor against breast cancer. The detailed analysis of the various risk factors such as various reproductive factors and anthropometry variables responsible for the rural urban differences in breast cancer differences is being conducted and would be published separately.
Most of the etiological studies have used current area of residence as a definition for rural , and limited studies which have taken early years of life spent  or place of the birth , in rural areas as a definition for "rural." However, current residence is not a good marker for studying the effect of the rural environment on the risk of breast cancer, as exposures in early life may be more important in the development of breast cancer compared to current exposures.  For instance, strenuous physical activity at a younger age can delay both menarche and onset of regular menstrual cycle.  Further, the individuals migrating from a rural area to urban area might not change their lifestyle and continue to adhere to rural life and therefore, they may continue to get protection from breast cancer even if they are currently residing in urban areas.
One of the explanations for the differences in the incidence of breast cancer in rural urban region may be differences in reproductive factors such as a woman in urban India has an average of 2.1 children in her lifetime when compared to 3.0 children in rural India. Furthermore, the obesity pattern is lower (8.6%) in rural areas as compared to the urban areas (28.9%) of women in India. 
Other possible candidates for explaining these strong rural urban differences include the established risk factors for breast cancer which have been identified in numerous studies conducted in western populations. Nulliparity and late age at first birth are the most consistently observed risk factors for breast cancer.  The risk among women who have their first child after the age of 30 is about twice that of women who have a first child before the age of 20. Similarly, women who start menstruating early in life, or have a late menopause, also have an increased risk of developing breast cancer,  possibly because of the increased number of ovulatory cycles and exposure to estrogens and other breast tissue proliferative hormones. It is also possible that extensive breast feeding reduces the risk of breast cancer by suppressing the number of ovulatory cycles, although the evidence based on studies conducted in western populations is unclear.  Association of oral contraceptives has shown inconsistent results with breast cancer risk. ,
The descriptive studies are necessarily rather speculative and elucidation of the causes of breast cancer occurrence can only be obtained by performing more detailed observational studies. Therefore, case-control studies are required to understand and quantify the factors responsible for these rural urban differences. There are few studies however, to understand these differences, , which have majorly discussed on the anthropometry and descriptive epidemiology.
A statistically significant increasing trend of 1.6% in breast cancer incidence rates has been observed by our study in Mumbai cancer registry in the last 15 years period. A similar increase, but not reaching statistical significance was observed in rural (Barshi) and urban (Aurangabad) registries indicating that lifestyle changes which are under operation in these areas may lead to a significant rise in breast cancer rates in the near future. Moreover, the urban population in India is expected to increase to >550 million by 2030 which will increase the burden of breast cancer. A close-to-doubling of incident cases by 2025 from 1300 mean cases per annum in 2001-2005 to over 2500 cases in 2021-2025 has been projected. 
Further, in medium HDI (includes India) and high HDI settings, decreases in cervical cancer incidence seem to be offset by increases in the incidence of cancer of the female breast. This is partly because a shift in lifestyles is causing an increase in incidence, and partly because clinical advances to combat the disease are not reaching women living in these regions. ,
Despite the remarkable differences in breast cancer incidence in rural and urban areas, mortality from breast cancer is almost similar in rural and urban India.  This could be attributed partly to lower accessibility to health care/treatment facilities in rural areas and to some extent to detection of breast cancer at an advanced stage in the rural areas.
The current study clearly demonstrates that living in a rural area decrease the risk of developing breast cancer. This indicates that the public health authorities should monitor the lifestyle which is peculiar to a rural area to help to prevent increasing burden of breast cancer. There is urgency to develop policies and the necessary infrastructure for early detection and improved medical care before breast cancer reaches the "epidemic" proportions seen in many high-resource settings. Preventive measures such as education for early detection, controlling obesity, having reproductive age below 25 years, and other lifestyle factors which appear to be more prevalent in rural areas can prove to be important public health strategies for breast cancer prevention and may potentially reduce the burden. Promotion of regular clinical breast examination for post-menopausal women in particular, may serve as important prevention strategies for reducing the mortality of breast cancer in India.
| » Acknowledgment|| |
We would like to thank all the staff members involved in data collection and data management and study participants that agreed to participate in the study.
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