Breast Cancer Survival Disparities between HIV+ Compared to HIV- Women Across Different Patient and Tumour Characteristics and Diverse Sub-Saharan African Settings

Background: Studies have shown increased mortality among HIV-positive women with breast cancer compared to HIV-negative women with breast cancer, but none has examined how this differential varies by patient or breast tumour characteristics.  Methods: ABC-DO study is a prospective cohort of incident breast cancer women recruited at diagnosis (2014-2017) in Namibia, Nigeria, South Africa, Uganda and Zambia. Detailed clinic-epidemiological data were collected at baseline. Participants were actively followed-up via 3-monthly telephone calls. Using Cox regression, we examined differences in overall survival by HIV status in the cohort, and across country and patient subgroups, adjusted for age at cancer diagnosis, tumour grade and stage at cancer diagnosis.   Findings: Among 1,635 women, 313 (19%) were HIV-positive, 1,184 (72%) were HIV-negative and 138 (9%) HIV-unknown. At breast cancer diagnosis, HIV-positive women were younger and had lower BMI than their HIV-negative counterparts, but had similar tumour stage, grade and receptor subtypes. At the end of the follow-up (January 1, 2019), a higher proportion of HIV-positive women (137 (44%)) had died compared to HIV-negative women (432 (37%)). Crude three-year survival was 9% lower for HIV-positive women (46% vs. 55% for HIV-negative women, hazard ratio (HR) 1·41; 95% CI: 1·15-1·74). The difference did not differ by age, BMI, tumour subtype or grade but was stronger in women with non-metastatic disease (52% HIV-positive vs. 63% HIV-negative women, adjusted HR 1·65: 1·30-2·10), whilst women with metastatic cancer had low survival regardless of HIV status.  Interpretation: The larger survival deficit among WLWH with non-metastatic breast cancer calls for a better understanding of the reasons underlying this differential e.g. biological mechanisms, health behaviours, detrimental HIV-breast cancer treatment interactions or higher HIV background mortality, to inform strategies for reducing mortality among this young patient group.  Funding: Susan G Komen, International Agency for Research on Cancer, National Cancer Institute and UK-Commonwealth Scholarships. Declaration of Interest: No declaration of competing interests. Ethical Approval: The ABC-DO study was approved by all institutional ethics committees (List 1 in Supplementary Material), and all women provided written or thumbprint informed consent, witnessed by the study interviewer.