Data for this Review were obtained from a comprehensive monograph8 and searches of PubMed, using the search terms “neoplasms”, “Africa”, and specific searches for each country. There were no language or date restrictions. Incidences cited are those from population-based cancer registries that have been published by the International Agency for Research on Cancer (Lyon, France).
ReviewPart I: Cancer in Indigenous Africans—burden, distribution, and trends
Introduction
Africa is the most heterogeneous and genetically diverse continent in the world,1 with an estimated population (in 2007) of 965 million people. Migrants from elsewhere in the world have settled in many parts of Africa, and large population movements to this region go back to the spread of the Greek, Roman, and Arabic peoples across North and East Africa up to 3000 years ago, with a more recent immigration of Europeans since the 1600s. Substantial numbers of Asian people (ie, Indians, Malays, and Chinese) have also migrated to Africa since the 19th century. As a result, most inhabitants of Africa would consider themselves indigenous, not only because of their historical links, but also because there would be no other place they would consider as their own.
About 41% of the African population is under the age of 15 years, compared with 28% worldwide, and fertility, despite recent declines, is about 4·7 births per woman compared with less than two births per woman in high-income countries (figure 1).2 According to WHO3 the major causes of death in Africa are infant and child mortality, maternal mortality, and communicable diseases (table 1).
Provision of services for the prevention and treatment of cancer has had a low priority with African governments and development agencies, which have focused on the more common health issues, such as communicable diseases and maternal and child mortality, which have been largely solved in the developed world (figure 1). Unfortunately, in Africa, these older, more common diseases co-exist with newer ones, most evidently AIDS, and also with some of the non-communicable diseases, including cancer. Although cancer accounts for only about 4% of deaths, this low proportion disguises the fact that cancer is not rare in absolute terms. Even ignoring the huge load of AIDS-related Kaposi's sarcoma, the probability of developing a cancer by the age of 65 years in a woman living in present-day Uganda (Kampala) or Zimbabwe (Harare) is only about 30% lower than that of women in western Europe, and the probability of dying from a cancer by this age is almost twice as high (table 2).
However, knowledge of cancer trends in Africa is inadequate, and, until recently, was based mainly on the work of pioneering clinicians and pathologists who reported case series of patients with cancer, encountered during their professional lives. Unfortunately, the frequency of cancers reported in case series is not consistent with their relative incidence in the population, so that comparisons (between centres or over time) based on such data do not give an accurate picture of the true variations in incidence. Pathology series under-represent cancers that are difficult to biopsy (such as cancers of the liver, pancreas, or brain), and hospital series are biased by the clinical facilities available (eg, radiotherapy series always include many cancers of the head and neck and of the cervix, and few gastrointestinal cancers). Furthermore, use of proportions (or percentages) of different cancers in clinical series as the statistic for comparison introduces a further issue: because the total must always equal 1 (or 100%), if one cancer is relatively common, all others in the series will seem to be rare.
The appropriate statistics for making comparisons of cancer risk between populations are incidence rates obtained from population-based cancer registries, which record all new cases of cancer that occur in a defined, enumerated population. Cancer registration has been slow to develop in Africa for various reasons, including defining residents of a particular area, identifying patients with cancer, and obtaining accurate diagnostic information for those with cancer. However, although cancer registration in Africa is more difficult than in developed countries, it is not impossible. Currently, cancer registries cover 11% of the population,4 although the quality of the data collected is variable.
Likewise, mortality statistics in Africa have been very sparse, because of the absence of comprehensive death registration in most countries. Since 1995, only three African countries (Mauritius, Egypt, and South Africa) have contributed to the WHO mortality database, and death registration in South Africa is estimated to be incomplete (50% in 1996, but has since improved).
As a result of the deficiencies of these registries, quantitative estimates of disease incidence and mortality patterns in Africa need to be obtained by various estimation methods.3, 5
Despite the limited data available, overall adult mortality in Africa was estimated to be improving before the start of the HIV and AIDS epidemic, and predictions have been made that it will improve in the long term.6 In addition to the devastating effects of HIV and AIDS in young adults, about 62% of older adults in Africa (eg, those over 45 years of age) die from non-communicable diseases, and about one in five deaths are due to cancer (table 3).
An estimated 650 000 new cases of cancer occurred in Africa in 2002 (of which 530 000 were in sub-Saharan Africa), with 311 000 cases in males and 338 000 in females.5 Table 4 shows the estimated number of new cases in 2002, and age-standardised incidence rates, for the six most common cancer types by region. In Africa as a whole, the most common cancers in males were Kaposi's sarcoma (12·9% of all cancers), and cancer of the liver (11·5%), prostate (9·5%), bladder (6·1%), non-Hodgkin lymphoma (5·7%), and oesophagus (5·2%). In females, the most common cancers were cancers of the cervix (23·3%) and breast (19·3%), Kaposi's sarcoma (5·1%), cancer of the liver (5·0%), non-Hodgkin lymphoma (3·8%), and cancer of the ovary (3·7%). World standardised incidence rates (all ages) are about 121 per 105 females and 126 per 105 males. The importance of infectious diseases in Africa, as noted above, means that as many as 36% of cancers in Africa are infection-related, exactly double the world average.7
There is enormous geographical diversity in the incidence of cancers between (and often within) the different countries of Africa, even for these common cancer types, as described in a recent monograph.8 Figure 2 shows the most common types of cancer in males, and in females, in different countries in Africa, as estimated in 2002.
This Review is the first of two papers, and focuses on the current knowledge of the distribution of different cancer types across Africa, and how these trends might have developed over time. The second paper will focus on the causes and prevention of these cancers in Africa.
Section snippets
Cancer of the cervix uteri
Cancer of the cervix is the most common cancer in Africa, with an estimated 79 000 new cases occurring each year (70 700 in sub-Saharan Africa, constituting 25·4% of cancers in females; table 4). Figure 3A shows the incidence of this cancer worldwide compared with in Africa.
The incidence of cervical cancer in Africa is highest in eastern and southern Africa (30–40 per 105 females); the rest of sub-Saharan Africa has a lower incidence (20–30 per 105 females), and north Africa has the lowest
Breast cancer
Figure 3B shows the estimated age-standardised incidence rates of breast cancer across the world in 2002.5 The incidence in Africa was generally low—most countries in Africa had an incidence below 35 cases per 105 females, with the highest incidence noted in South Africa (35·0 per 105 females). In total, there were an estimated 65 000 new cases of breast cancer in Africa in 2002, which constituted 19% of female cancers (compared with 79 000 cases of cervical cancer). There were an estimated
Kaposi's sarcoma
Before the epidemic of HIV and AIDS in Africa, the incidence of Kaposi's sarcoma varied greatly, with the highest incidence noted in central Africa and lower incidences noted in northern and southern Africa.27, 28 From the sparse data available, Kaposi's sarcoma in regions of central Africa was shown to be as common as colon cancer in developed countries.29 A geographical association seems to exist with the prevalence of human herpes virus-8 (HHV-8), now regarded as a necessary cause for the
Liver cancer
Early reports from Africa noted the frequent occurrence of liver cancer,34 and this disease is still one of the most common cancers in both males and females in Africa, although its relative importance has decreased with the emergence of newer cancers, notably the large increase in the incidence of Kaposi's sarcoma resulting from the epidemic of HIV-AIDS. Liver cancer is now the fourth most common cancer in Africa, with an estimated 52 000 cases in 2002.5 Most are hepatocellular carcinomas.
The
Non-Hodgkin lymphoma
About 25 000 new cases of non-Hodgkin lymphoma in sub-Saharan Africa (and 5000 cases in north Africa) occurred in 2002. In most African populations, non-Hodgkin lymphoma is rare, with incidence rates well below those in Europe and North America, although it is often perceived as a common cancer in Africa, because it ranks fifth in relative frequency. Most non-Hodgkin lymphomas in Africa are of the B-cell type, and clinical series show an excess of high-grade lymphomas and a deficit of nodular
Prostate cancer
In sub-Saharan Africa, 26 800 cases of prostate cancer were estimated in 2002, constituting 10·6% of all cancers in males.5 This cancer is less common in north Africa (2900 cases [4·8% of all cancers in males]) than in other African regions. The high incidence (and mortality) in some African populations is also present in other populations of African descent. In the USA, the incidence of and mortality from prostate cancer are about 72% higher in black people than in white people,8 and African
Stomach cancer
About 13 800 cases of stomach cancer in males and 12 000 in females were estimated in Africa in 2002. The age-standardised incidence in males varied, from three cases per 105 in west Africa, 7–8 per 105 in southern and east Africa, to 13 per 105 in central Africa. In west Africa, where incidence rates of stomach cancer are low, the male to female ratio is 0·9; however, there is a male predominance in all other areas (table 4). Despite the generally low incidence of stomach cancer in Africa,
Bladder cancer
An estimated 25 600 cases of bladder cancer were recorded in Africa in 2002, 55% of which were in north Africa, which has the highest incidence of bladder-cancer mortality worldwide. Although the incidence of bladder cancer is high in most countries in north Africa, the incidence is especially remarkable in Egypt, where in males, the estimated incidence (age-standardised rate 37·1 per 100 000) and mortality (age-standardised rate 34·0 per 100 000) are extremely high. Although the rates of
Cancer of the oesophagus
Cancer of the oesophagus shows a remarkable geographical distribution, and is one of the most common cancers in southern and east Africa (12–25 per 105 males), but is rare in west Africa (1–2 per 105 males; figure 6).
There is a strong geographical correlation between the incidence of oesophageal cancer in males and females. Certain areas of high risk have been reported in Kenya, and in the former Transkei homeland in the Eastern Cape province of South Africa, where the incidence was as high as
Conclusion
Cancer has been an under-recognised issue in Africa. The HIV epidemic has arguably caused the biggest change in cancer patterns, with Kaposi's sarcoma now the most common cancer in males and the third most common cancer in females. Furthermore, certain cancer types, such as cancer of the lung, breast, prostate, and oesophagus, have increased substantially as a result of changes in exposures to common carcinogens, and due to changing lifestyles. Cancers and other non-communicable diseases are
Search strategy and selection criteria
References (56)
KSHV (HHV8) infection
J Infect
(2000)Persistent immunologic stimulation as a factor in oncogenesis with special reference to Burkitt's tumour
Ann J Med
(1970)Is endemic Burkitt's lymphoma an alliance between three infections and a tumour promoter?
Lancet Oncol
(2004)- et al.
Epidemiology of prostate cancer in Africa: another step in the understanding of the disease?
Curr Probl Cancer
(2007) - et al.
Alu insertion polymorphisms and human evolution: evidence for a larger population size in Africa
Genome Res
(1997) The world health report 2004. Changing history
(2004)The evolution of the population-based cancer registry
Nat Rev Cancer
(2006)- et al.
GLOBOCAN 2002: cancer incidence, mortality and prevalence worldwide
(2003) Population and mortality after AIDS
The global health burden of infection-associated cancers in the year 2002
Int J Cancer
(2006)
Morbidity from cancer in the United States: parts I and II
(1959)
Trends in cancer of the cervix uteri in Sweden following cytological screening
Br J Cancer
(1999)
Cancer patterns and risk factors in the African population of southwestern Zimbabwe, 1963–1977
Cancer Epidemiol Biomarkers Prev
(1994)
Trends in cancer incidence in Kyadondo County, Uganda, 1960–1997
Br J Cancer
(2000)
Incidence of histologically diagnosed cancer in South Africa, 1998–1999
(2004)
Cancer mortality among North African migrants in France
Int J Epidemiol
(1996)
Cancer mortality among sub-Saharan African migrants in France
Cancer Causes Control
(1995)
Cancer mortality in African and Caribbean migrants to England and Wales
Br J Cancer
(1992)
Breast cancer at diagnosis in women of Africa and the Middle East
Cancer survival in a southern African urban population
Int J Cancer
(2004)
Cancer survival in Kampala, Uganda
Br J Cancer
(2005)
SEER cancer statistics review, 1975–2004
Widening disparity in survival between white and African-American patients with breast carcinoma treated in the US Department of Defense Healthcare system
Cancer
(2003)
Histopathology of breast cancer among African-American women
Cancer
(2003)
Cited by (0)
Copyright © 2008 Elsevier Ltd. All rights reserved.