The review of genetic screening services and common BRCA1/2 variants among South African breast cancer patients

The South African genetic screening services for breast cancer comprise targeted and comprehensive tests that screen for the presence of genetic alterations. Clinically, these variants determine the risk of disease development as well as treatment approaches best suited for carriers. The current targeted tests screen for seven pathogenic sequence variants, which are mainly common among Whites, a population that constitutes 9.1% of South Africa. However, these tests are offered to all patients despite consistent negative results observed among Blacks, Indians, and Mixed ancestry (known as Coloreds in South Africa). Consequently, Blacks, White, and Colored patients who potentially carry other variants receive unbefitting treatment, resulting in poor clinical response, recurrence, and high mortality. This review aimed to identify the presence and incidence of pathogenic variants in BRCA1/2 previously reported in all South African populations. We selected literature using a scoping review approach, from which we included eight articles and two reports. Overall, we identified 59 BRCA1 and 60 BRCA2 pathogenic sequence variants from a cohort of 5709 patients and unknown patients from 90 families. The most reported variant was BRCA2 c.7943delG, which was common in White and Colored patients. None of the seven common variants was reported in either Blacks or Indians, which demonstrates the urgency to tailor genetic tests which are optimal for all South African patients and present a range of variants which could serve as diagnostic targets for Black, Indian, and Colored patients.

Genetic trends and common BRCA1/2 pathogenic sequence variants in black African and Indian breast cancer patients presenting at Inkosi Albert Luthuli Central Hospital, KwaZulu-Natal, South Africa

BACKGROUND

Hereditary breast cancer is characterised by the presence of a pathogenic sequence variant passed from one generation to the next. These cancers are aggressive, develop early, and account for 5 - 10% of all breast cancer cases. In South Africa (SA), the common variants that predispose to hereditary breast cancer have been well documented among white patients and form part of screening panels during targeted testing. For non-white patients, common variants are not well understood, and as such, all populations are offered the same test optimised for white patients. This carries a risk of misdiagnosis, the consequences of which include recurrence and increased mortality.

OBJECTIVES

To retrospectively describe genetic trends in the black African and Indian breast cancer patients from KwaZulu-Natal Province, SA.

METHODS

We reviewed clinical and genetic data of breast cancer and high-risk patients who consulted at Inkosi Albert Luthuli Central Hospital between 2011 and 2021. Inclusion criteria were based on clinical and demographic characteristics as defined by SA clinical guidelines.

RESULTS

Black African patients were young (mean 37.6 years, standard deviation 11.16) and had the majority of triple-negative tumours (37.5%). Indians represented 50% of bilateral breast cancers and of high-risk individuals. We identified 30 pathogenic BRCA1/2 sequence variants, four large genomic rearrangements and 13 variants of unknown significance. Twenty black patients carried 12, 13 white patients carried 4, 25 Indian patients carried 16, and 3 coloured patients carried 3 pathogenic sequence variants. The most frequent variants were BRCA2 c.5771_5774del, p.Ile1924fs among black patients, BRCA2 c.7934del, p.Arg2645fs among white patients, and BRCA2 c.8754+1G>A among Indian patients. None of the founder mutations common in white patients was reported in either black, Indian or coloured patients, which explains why black, Coloured and Indian SA patients consistently test negative during targeted screening.

CONCLUSION

This study highlights unique genetic trends for SA populations and the need for more inclusive targeted tests that are optimal for these populations.

Recent trends in hereditary breast cancer incidence by race and age in KwaZulu-Natal, South Africa: An 11-year single-centre retrospective study (2011-2021)

Breast cancer incidence has increased globally in the last decade, especially in low- and middle-income countries. In Sub-Saharan Africa, breast cancer trends have been described only in a few populations owing to the scarcity of population-specific data. Using data collected between 2011 and 2021 at Inkosi Albert Luthuli Central Hospital, this retrospective study describes demographic and genetic trends for hereditary breast cancer patients in the KwaZulu-Natal province, South Africa. Six hundred and forty-five patients were included, of whom 44.3% were Black, 36.8% Indian, 15.6% White and 3.2% Coloured. The number of annual new cases increased from eight in 2011 to 145 in 2021, with a notable increase among Blacks. The mean onset age was 46 years, and Black patients were diagnosed ~10 years earlier than White and Indian patients. Triple-negative breast cancers accounted for 20.3% of hereditary cases, and 51.1% of them were Black. Bilateral and recurrent breast cancers constituted 7.4%, while pathogenic sequence variants in BRCA1/2 were reported in 10.4% of all patients, and the majority were Blacks and Indians. Overall, the KwaZulu-Natal province has seen an increase in hereditary breast cancer incidence in the past decade. Despite testing negative for pathogenic sequence variants, Black women frequently presented with breast cancers that are BRCA1-like, while Indians presented with extensive family history. This suggests that South African patients may require unique approaches to interventions, such as early detection and awareness programs among Blacks and increased genetic screening among Indians.