SCIENCE sciencemag.orgPHOTO: STRINGER/REUTERS/NEWSCOM
By Timothy R. RebbeckC
ancer is an increasing global pub-
lic health burden. This is especially
the case in sub-Saharan Africa (SSA);
high rates of cancer—particularly of
the prostate, breast, and cervix—char-
acterize cancer in most countries in
SSA. The number of these cancers in SSA is
predicted to more than double in the next
20 years ( 1 ). Both the explanations for these
increasing rates and the solutions to address
this cancer epidemic require SSA-specific
data and approaches. The histopathologic
and demographic features of these tumors
differ from those in high-income countries
(HICs). Basic knowledge of the epidemiology,
clinical features, and molecular characteris-
tics of cancers in SSA is needed to build pre-
vention and treatment tools that will address
the future cancer burden. The distinct dis-
tribution and determinants of cancer in SSA
provide an opportunity to generate knowl-
edge about cancer risk factors, genomics, and
opportunities for prevention and treatment
globally, not only in Africa.
The most frequent cancers in African coun-
tries include prostate, lung, liver, leukemia,
non-Hodgkin’s lymphoma, and Kaposi's sar-
coma in men and breast and cervical cancer
in women (see the figure). Distinct risk fac-
tors in SSA contribute to the understanding
of cancer etiology in ways that may not be as
easily studied in HICs. For example, the ob-
servation of high rates of Burkitt's lymphomain SSA launched the research that identified
Epstein-Barr virus as the causal agent of
Burkitt's lymphoma ( 2 ), thus providing some
of the earliest knowledge about the infectious
and molecular etiology of cancer. Similarly,
the high prevalence of HIV infection and the
attendant large number of HIV-associated
cancers in SSA have enabled research that
has led to understanding of the causes and
treatment of cancers exacerbated by HIV
infection, including cervical cancer, Kaposi's
sarcoma, and non-Hodgkin's lymphoma ( 3 ).
Patients with cancer in SSA are often di-
agnosed when their disease is in advanced
stages. This is in part a consequence of inad-
equate resources for cancer prevention and
early detection. Delayed diagnosis coupled
with inadequate treatment options is a ma-
jor reason for the continent’s cancer mortal-
ity rates, which are 1.5- to 4-fold higher than
in HICs for leading cancers ( 1 ). Studies that
focus on features of late-stage and aggressive
disease will be required to better understand
how to manage such disease states. This re-
search is required to develop and implement
early detection and treatment modalities that
can be implemented in low-resource settings
such as SSA, where availability of laboratory
or imaging technologies is limited.
Although molecular and other biologi-
cal data that address cancer etiology and
progression in SSA are limited, emerging
evidence suggests that distinct tumor histo-
pathology, tumor subtypes, and molecular
signatures exist in SSA. For example, Nige-
rian breast cancer cases were defined by in-
creased mutational signature associated with
deficiency of the homologous recombination
DNA repair pathway, pervasive mutationsin the tumor suppressor gene TP53, muta-
tions in GATA binding protein 3 (GATA3),
and greater genomic mutational burden (in-
dicating aggressive biology), compared with
breast tumors from African Americans or
Caucasians ( 4 ). This suggests different tumor
etiologies by race or geography, perhaps re-
flecting particular environmental exposures
to carcinogens, and may provide knowledge
about the spectrum of breast cancer molec-
ular phenotypes that may be composed of
distinct molecular subtypes and represent
different frequencies of known subtypes in
non-Africans. Knowledge of these differences
can lead to optimized monitoring and treat-
ment across all populations.
Early age at diagnosis is a hallmark of
cancer in SSA, which has been proposed to
reflect a higher rate of hereditary cancer in
SSA. This is supported by the observation
that although 29% of SSA women and 33% of
Caucasian women are between ages 25 and
49, 58% of SSA women are diagnosed with
breast cancer before they are 50 years old,
compared with 21% of Caucasian women ( 5 ).
Breast tumors in SSA Black cases are twice as
likely as SSA Caucasian cases to be the triple-
negative subtype, meaning that the estrogen,
progesterone, and HER2 receptors are not
expressed by the breast cancer cells, making
them highly aggressive and difficult to treat
( 6 ). These molecular features are hallmarks
of hereditary cancers; genetic testing for
pathogenic sequence variants in the tumor
suppressor genes breast cancer 1 (BRCA1)
and BRCA2 in a series of Nigerian breast can-
cer cases suggested that the rate of cancers
in women with BRCA1 or BRCA2 germline
pathogenic sequence variants is higher than
in Caucasian populations ( 7 ). Although large
population studies of hereditary cancer in
SSA do not yet exist, BRCA1 and BRCA2 mu-
tations of SSA origin are also found in Afri-
can Americans, and the type of mutations in
BRCA1 and BRCA2 differs between SSA and
non-SSA populations ( 8 ).
Generation of knowledge about cancer in
SSA will lead to both improved cancer pre-
vention and treatment. Protocols and net-
works are being formed to study cancer in
SSA patients and translate this knowledge to
health care in SSA ( 9 ). These protocols may
begin with those used in HICs but must be op-
timized to low-resource settings, which have
limited access to equipment, trained person-
nel, and therapies. Although the availability
of basic research infrastructure is more lim-
ited in SSA than in HICs, there are numerous
basic science and translational research insti-
tutes in SSA, including those that can addressGLOBAL HEALTHCancer in sub-Saharan Africa
Knowledge of cancer in Africa brings needed
diversity to improve health worldwide
Dana-Farber Cancer Institute and Harvard T. H. Chan
School of Public Health, Boston, MA, USA.
Email: [email protected]Research is needed to understand the
projected increase in cancer incidence
and mortality in sub-Saharan Africa.3 JANUARY 2020 • VOL 367 ISSUE 6473 27
Published by AAAS