The association of HIV status with triple-negative breast cancer in patients with breast cancer in South Africa: a cross-sectional analysis of case-only data from a prospective cohort study.

Background: Breast cancer is the most common malignancy diagnosed among women in South Africa, with the aggressive triple-negative subtype comprising approximately 15% of breast cancers in this population. South Africa has the largest population of people with HIV in the world. This study aims to evaluate the association between HIV status and the proportion of patients with breast cancer with the triple-negative subtype.

Methods: We did a cross-sectional analysis of case-only data from the South African Breast Cancer and HIV Outcomes (SABCHO) study, a prospective cohort study recruiting patients with newly diagnosed breast cancer at six public hospitals in South Africa. We analysed data from patients who enrolled in SABCHO between Jan 1, 2015, and Jan 18, 2022. Women aged 18 years or older with newly diagnosed and histologically confirmed invasive breast cancer were eligible. Participants were classified as HIV-positive or HIV-negative by use of an ELISA-based HIV test done at the time of enrolment. We developed multivariable logistic regression models to test for an association between HIV status and the proportion of triple-negative relative to non-triple-negative breast cancers while adjusting for demographic and reproductive risk factors.

Findings: Of the 4122 patients enrolled in the SABCHO cohort within our study timeframe, 239 patients were excluded due to unknown breast cancer subtype (n=141), HIV status (n=97), or race (n=1). 3883 women with breast cancer were included in the study, of whom 637 (16·4%) had triple-negative breast cancer, 894 (23·0%) were HIV-positive, and 186 (4·8%) had triple-negative breast cancer and HIV. Triple-negative breast cancer accounted for 186 (20·8%) of 894 breast cancers among women who were HIV-positive and 451 (15·1%) of 2989 breast cancers among women who were HIV-negative (p<0·0001). In the fully adjusted logistic regression model, HIV-positive status was associated with an increased proportion of triple-negative breast cancer (adjusted odds ratio [OR] 1·39, 95% CI 1·12-1·74, compared with women who were HIV-negative). When compared with women who were HIV-negative, the association between HIV-positive status and the proportion of triple-negative breast cancer was strongest among the subgroup of women with a duration of HIV infection of 2 years or longer (1·57, 1·23-2·00) and those on antiretroviral therapy (ART; 1·47, 1·16-1·87).

Interpretation: Patients with breast cancer and chronic HIV who are on ART are more likely to have triple-negative breast cancer than patients with breast cancer without HIV. This association is independent of age, race, and reproductive factors.

Funding: US National Institutes of Health, University of the Witwatersrand, South Africa Medical Research Council Common Epithelial Cancers Research Center, Conquer Cancer Foundation, and Varmus Global Scholars Fund.