Emerging breast cancer epidemic: evidence from Africa
© BioMed Central Ltd 2010
Published: 20 December 2010
Cancer is an increasingly important public health problem in developing countries, including Africa . As public and professional awareness of the cancer problem has grown, so has interest in the pattern of disease presentation, its epidemiology and treatment outcome. To date, however, there has been limited research about breast cancer in Africa. In the absence of systematic population-based cancer registration, most information has come from small clinical and pathology case series and the bias inherent in these types of studies has influenced current understanding of the pattern and characteristics of breast cancer in Africa.
In this communication, we review the evidence for an emerging epidemic of breast cancer in Africa, its risk factors and likely future course. We conclude that, despite limited data, rising incidence of breast cancer is being driven by increasing life expectancy, improved control of infectious diseases, and changing lifestyle, diet, physical activity and obstetric practices. We also review current beliefs about hormone receptor subtypes of breast cancer in Africa and suggest that this is probably not systematically different from the pattern in other populations after adjusting for factors such as age and that the reported differences are related to poor tissue handling and laboratory processing practices.
Global trends in cancer epidemiology
From an estimated 12 million new cases and 7.6 million deaths in 2008, the incidence of cancer worldwide is expected to rise to 26.4 million with 17 million deaths by 2030. Most of these new cases of cancer are expected to occur in the developing world, particularly India and China . Current data suggest that cancer kills more people than HIV/AIDS, tuberculosis and malaria combined, but this overall picture hides significant variations in incidence in different parts of the world. Whereas cancer incidence is certainly rising in all developing countries, the poor control and persistence of old infectious diseases and emergence of new ones in Africa means that infections remain the major source of morbidity and mortality in this part of the world compared to Asia and Latin America, where the impact of non-communicable diseases has now become more predominant.
Demographic change and breast cancer in Africa
Epidemiological risk factors of breast cancer
Incidence is not likely to be constant, however, and the direction of its change is related to changes in the epidemiological risk factors for breast cancer . The incidence of breast cancer starts to increase at about the age of 20 years and rises rapidly to about the age of 50 years, when the rate of increase reduces somewhat, and by 75 years of age the incidence starts to decline. This pattern has been observed in all populations with adequate data for analysis. The established risk factors for breast cancer include age, sex, age at onset of menarche, age at first full-term pregnancy, parity, breast feeding, age at onset of menopause, obesity and physical activity . The direction of change in these risk factors in Africa is towards increasing incidence of breast cancer [4, 5]. Age at onset of menarche is reducing because of improved nutrition and reduced physical activity. Increased demands for education and modern lifestyle choices are delaying the age at first full-term pregnancy and the fertility rate of African women, which is also contributing to reduced total lifetime breast feeding duration.
Analysis of African breast cancer cases and controls studied in Ibadan showed an association with height (adjusted odds ratio 1.05, 95% confidence interval 1.01 to 1.08), a marker for nutrition in early life and with waist-hip ratio (adjusted odds ratio 2.67, 95% confidence interval 1.05 to 6.80) [6, 7].
A birth cohort analysis of the control participants recruited from 1998 to 2007 as part of a case-control study of the genetic risk factors of breast cancer in African women clearly demonstrates the effect of birth cohort on the epidemiological risk factors of breast cancer in African women. Comparing women born in the decades before 1940 with those born after 1960, the age at onset of menarche fell from 16.4 years to 15.3 years. Similarly, parity declined from 6 to 4 while the cumulative duration of breast feeding fell from an average of 120 months to 60 months . These parameters still have some way to go before approximating western figures, suggesting that further changes will contribute to further increases in breast cancer incidence.
Early onset breast cancer in African women
Breast cancer among young women in any population tends to be clinically and pathologically aggressive, with rapid progression and a higher mortality rate compared to older women . Because the African population is predominantly young and African breast cancer patients tend to be young, the pattern of breast cancer that presents to practitioners in Africa is mostly aggressive in clinical course with a high fatality rate. This is not an intrinsic African pattern of breast cancer, rather another manifestation of the demographic structure of the population.
Molecular subtypes of breast cancer in Africa
Another area of controversy in breast cancer in Africa is the characterization of the hormone receptor subtypes in the patient population. Several studies have suggested that African breast cancers are predominantly hormone receptor poor . Pathologists and researchers working in low resource countries have encountered problems related to poor preparation and fixation of tissue samples, which has often led to inability to apply advanced immunohistochemical and molecular biology techniques . These problems include poorly quality specimens from large and necrotic tumors, prolonged delay before fixation, questionable quality of fixative materials, prolonged stay in fixative (often for several weeks), poor laboratory techniques and quality assurance/quality control practices .
More systematic studies of breast cancer in Africa have not confirmed the suggestion that African breast tumors are predominantly receptor poor [11, 12]. Given that similar claims have been made of breast cancer subtypes in other parts of the world and these have also been found to be untrue after careful studies and the wide variation in genetic and environmental characteristics of the different low resource environments where these observations had been made, poor tissue preparation rather than intrinsic biological characteristics is the likely reason for the results seen in some studies [11, 13]. Compounding the problem of immunohistochemistry of breast tumors is the lack of methodological standardization even in developed countries, resulting in up to 20% variation in false positives and negatives and suboptimal utilization of the information currently generated by receptor assays .
Significance of these controversies
Despite improved understanding of the epidemiology of breast cancer and the impact of the current African demographic pattern on the age distribution, breast cancer affects many young and middle-aged African women at the most active phase of their social and economic life, resulting in significant economic, social, physical and psychological harm . Research and implementation of methods of effective early detection, effective but low-cost, low-tech treatment of early onset breast cancer, and management of the social, economic and psychological sequelae of the disease are urgently required [15, 16]. African breast cancer patients must be offered hormonal therapy where the hormone receptor status is unknown because of lack of immunohisto-chemical services. These are relatively inexpensive with tolerable toxicity profiles. Development of managed 'hub and spoke' regional pathology laboratory model systems that support several hospitals will improve the quality of pathology services and reduce cost. Training of clinicians and laboratory technicians to ensure proper tissue sampling and fixation is critical and of the foremost importance . Much work remains to be done in order to better understand breast cancer in African women.
This article has been published as part of Breast Cancer Research Volume 12 Supplement 4, 2010: Controversies in Breast Cancer 2010. The full contents of the supplement are available online at http://breast-cancer-research.com/supplements/12/S4
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