Journal Club - Faculty of Public Health, KKU

Why the findings about cancer in sub-Saharan Africa are of general interest?

Journal club – Faculty of Public Health, Khon Kaen University
February 2020 (2563)

 

Why the findings about cancer in sub-Saharan Africa are of general interest?

The character of cancer diseases differs considerably over continents and regions. To know about this helps to fully understand the many facets of this major public health problem.

A recent short essay about ‘Cancer in sub-Saharan Africa’ raised the point that cancer is a global health problem but important characteristics of the disease differ considerably between continents. This was illustrated in reviewing differences in cancer occurrence in sub-Saharan Africa (SSA) compared with high-income countries (HICs)(1). The risk of females in SSA to developing cervix cancer is much higher than for those in HICs. The proportion of newly diagnosed cervix cancer in SSA amounts to 23.3% compared to HICs with 2.1% in 2018, based on the total population. Less obvious but still remarkable differences exist for a number of other cancer locations (HICs percentages given in parenthesis): Esophagus 2.1.% (0.6%), Kaposi’s sarcoma[1] 2.4% (<0.1%) and liver 2.8% (1.5%). For males from SSA prostate cancer with 21.5% (18.9%) dominates cancer incidence like in HICs. Similarly, to females, males from AAS suffer from esophagus cancer with 4.2% (1.8%), Kaposi’s sarcoma with 6.2% (0.1%) and liver cancer with 7.2% (2.9%). All these cancer locations appear more often than in HICs. To know the differences in the epidemiological features for cancer in Africa compared to HICs is of importance for prevention and therapy for Africa. Particular conditions in the overall environment as risk factors must be taken into account and restrictions due to limited resources in prevention and early detection must be lessened. That especially is necessary in view of the 1.5- to 4-fold higher mortality for outstanding cancer locations in AAS compared to HICs.

What can be learned from findings in Africa for other parts of the world?

Beyond the importance of knowing about the epidemiological characteristics of cancers in Africa and developing strategies and means to improve prevention and therapy for SSA populations and cancer patients, the histopathology, molecular factors and genetics of cancer types in Africa are of interest for HICs as well (and as it might be added here, also for South East Asia and Asia as a whole). Findings obtained in Africa are suited to widen the understanding of the dynamics of cancer developments in other parts of the world. For instance, the identification of the Epstein-Barr virus, as causing agent for Burkitt’s lymphoma[2] (2), is one of the well-known evidence that

[1] Cancer producing spots of abnormal tissue under the skin, around the mouth, nose, throat, within lymph nodes and other organs. The cause is a herpesvirus transmitted through sexual intercourse or under immunotherapy.
[2] Cancer of the lymphatic system, especially B lymphocytes. 

virus, an infectious agent, is linked to a cancer site. Cancer as such is considered to be a ‘chronic’ disease, or as it is called more often now a ‘non-communicable disease (NCD)’, thus causing difficulties in the definition of what is an infectious- compared to an NCD disease. More recently the higher incidence of cervical cancer, Kaposi’s sarcoma and non-Hodgkin’s lymphoma[3] in connection with HIV treatment in Africa(3) is another interesting finding of general significance.

The interesting pattern of molecular and genetic conditions for SSA cancer

The supposed link of infectious agents, here virus, and cancer isn’t the only startling facet being made aware from observations at SSA. Particular molecular and genetic conditions observed in SSA, seemingly being different from cancer patients in other parts of the world, and should being taken in consideration while monitoring the cancer manifestations and caring for cancer patients everywhere else. Female SSA breast cancer incidence for instance doesn’t differ with 25.8% (24.5%) far from HICs, but SSA Black cancer patients experience breast cancer diseases which are often more aggressive and treatment resistant than SSA Caucasian breast cancer patients(4). It seems that not only pathological characteristics differ for cancer diseases between continents but also hereditary risks factors. Research in genetic risk factors in African populations are still rare but probably cancer risk due to genetic mutations might be higher for African females compared with their Caucasian counterparts. A study conducted in Nigeria found that a ,loss-of function mutation for BRCA1 and BRCA2’[4] was higher for black African- than for Caucasian patients(5). A similar result was obtained in comparing ‘loss-of function BRCA1 and BRCA2 mutations’ in African Americans females with SSA background with non-SSA populations(6). Similar results were obtained for ‘the homologous recombination DNA repair pathway’, TP53,[5] and GATA3[6] (7). The higher prevalence of genetic risk factors seems not be restricted to African SSA females, and here established in particular for breast cancer. SSA males also face a similar risk when it comes to prostate cancer, which has the highest assumed incidence with 21.5% (18.9%) of all cancers in males. For instance, a lower occurrence of the risk allele 2q37 is present in Caucasians compared to African males and African Americans(8).

Comment

Research results about cancer in SSA might not only be of benefit for the SSA population, but as pointed out also for ‘the diaspora (primarily in North America and Europe). Of major importance for South East Asia including Thailand are the hints given in this short communication and could be a guideline for similar research attempts by the research community around here. One of the objectives of the author seemed to be to make the international research community aware of a  

[3] Cancer developed from lymphocytes.
[4] The BReast CAncer genes (BRCA) type 1 and 2 are tumor suppressor genes repairing damaged DNA. Loss of function of the genes results in an increase in the risk of breast cancer since damaged DNA is not properly repaired.
[5] TP53 is a tumor suppressive gene.
[6] GATA3 is a transcription factor which is of importance for genes involved in biological and clinical functions. 

number of basic science and translational research institutions in SSA’. To know about these research centers is promising since it shows, that academic colleagues from Africa now are supplementing the international research community in force. It certainly is worthwhile to elaborate on additional aspects like genetic and molecular attributes of the disease. However, the prominence of socio-economic and environmental risk factors in the spectrum of the cancer development should be kept in mind and weighted against what might be termed molecular epidemiology(9, 10). For instance, under the headline ‘Cancer in SSA’ one might have expected some words about the cultural background related to sexual behavior in connection with the high incidence of cervix cancer and the role of smoking in the cancer occurrence at SSA. The incidence of lung cancer in SSA males with 4.6% against 12.0% of males in HICs is rather low. Is smoking not that common in SSA or is life expectancy too short so that lung cancer is mainly observed in the smaller proportion of elderly SSA males? Unfortunately, the legend of the table displayed does not mentioned whether the data are age-standardized or not and by trying to clarify that by going to the reference given one is lost in numerous sub-websites, of which it is difficult to identify the one the author referred to. Last not least a scientific contribution should be politically neutral. The euphemism referring to the largely illegal migrants from Africa now in Europe as ‘diaspora’ is not well taken. 

Literature:

1. Rebbeck TR. Cancer in sub-Saharan Africa. Science. 2020;367(6473):27-8.

2. Burkitt D. A sarcoma involving the jaws in African children. Br J Surg. 1958;46(197):218-23.

3. Chinula L, Moses A, Gopal S. HIV-associated malignancies in sub-Saharan Africa: progress, challenges, and opportunities. Curr Opin HIV AIDS. 2017;12(1):89-95.

4. McCormack VA, Joffe M, van den Berg E, Broeze N, Silva Idos S, Romieu I, et al. Breast cancer receptor status and stage at diagnosis in over 1,200 consecutive public hospital patients in Soweto, South Africa: a case series. Breast Cancer Res. 2013;15(5):R84.

5. Zheng Y, Walsh T, Gulsuner S, Casadei S, Lee MK, Ogundiran TO, et al. Inherited Breast Cancer in Nigerian Women. J Clin Oncol. 2018;36(28):2820-5.

6. Rebbeck TR, Friebel TM, Friedman E, Hamann U, Huo D, Kwong A, et al. Mutational spectrum in a worldwide study of 29,700 families with BRCA1 or BRCA2 mutations. Hum Mutat. 2018;39(5):593-620.

7. Pitt JJ, Riester M, Zheng Y, Yoshimatsu TF, Sanni A, Oluwasola O, et al. Characterization of Nigerian breast cancer reveals prevalent homologous recombination deficiency and aggressive molecular features. Nat Commun. 2018;9(1):4181.

8. Lachance J, Berens AJ, Hansen MEB, Teng AK, Tishkoff SA, Rebbeck TR. Genetic Hitchhiking and Population Bottlenecks Contribute to Prostate Cancer Disparities in Men of African Descent. Cancer Res. 2018;78(9):2432-43.

9. Schelp FP,Kraiklang R, Muktabhant B, Chupanit P, Sanchaisuriya P. Public health research needs for molecular epidemiology and to emphasize alpha-2-macroglobulin be a meaningful biomarker? F1000Res. 2019.

10. Slattery ML. The science and art of molecular epidemiology. J Epidemiol Community Health. 2002;56(10):728-9.