Groundbreaking study finds new genes in black women causing breast cancer

Black South African women have been found to have two new genes that make them susceptible to breast cancer.

Research done by the Sydney Brenner Institute for Molecular Bioscience (SBIMB) at the Witwatersrand University found genetic factors that contribute to about 30% of breast cancer (BC) cases in South Africa.

“These genes have not been associated with the disease before, which is an important advance in understanding breast cancer risk and biology in women of African ancestry,” said Dr Mahtaab Hayat, a lead author of the study.

The two new genetic variants were identified in black South African women with breast cancer enrolled in the Johannesburg Cancer Study, compared to women without cancer in the Africa Wits-INDEPTH Partnership for Genomic Research (AWI-Gen) study.

Breast cancer is the second-most common cancer in South Africa and the most common cancer in women globally, with genetic factors contributing to about 30% of cases.

“Our study makes a compelling case for investing in genomic research rooted in African contexts,” said Hayat.

All participants were from the Soweto region, with 2,485 population cases and 1,101 control cases. The South African BC cases and controls were well-matched and clustered, while the non-South African samples and West African populations were distinct from South African populations.

The Genome-Wide Association study (Gwas), which is the first to focus on black women on the continent, was published in the journal Nature Communications. It brings to the fore the importance of deepening knowledge about the genetic basis of the disease.

In the past, most breast cancer genetics research has focused on European and Asian populations, with studies of African ancestry limited primarily to African-American women, who largely descend from West African populations.

A tool that estimates lifetime cancer risk based on DNA, the polygenic risk score (PRS), performed poorly in distinguishing South African women with breast cancer from those without. Dr Jean-Tristan Brandenburg, also in the SBIMB and a lead author, said this was a result of the mechanism not being tailored for the black population.

“This is because most PRSs were developed in European populations, and their inaccuracy in African populations highlights the urgent need for ancestry-specific tools in cancer risk prediction,” Brandenburg said.

African populations have more genetic variation than any other population in the world, but they have been significantly underrepresented in genomic research. This means the global understanding of disease risk and the tools and treatment developed from it are limited.

“The study reveals that more people can benefit from genetic discoveries. It proves that new risk factors are still out there, waiting to be found,” says Hayat.

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