Breast cancer survival and survival gap apportionment in sub-Saharan Africa (ABC-DO): a prospective cohort study

Abstract

Background: Breast cancer is the second leading cause of death from cancer in women in sub-Saharan Africa, yet there are few well characterised large-scale survival studies with complete follow-up data. We aimed to provide robust survival estimates in women in this setting and apportion the survival gaps.

Methods: The African Breast Cancer-Disparities in Outcomes (ABC-DO) prospective cohort study was done at eight hospitals across five sub-Saharan African countries (Namibia, Nigeria, South Africa, Uganda, and Zambia). We prospectively recruited women (aged ≥18 years) who attended these hospitals with suspected breast cancer. Women were actively followed up by use of a telephone call once every 3 months, and a mobile health application was used to keep a dynamic record of follow-up calls due. We collected detailed sociodemographic, clinical, and treatment data. The primary outcome was 3-year overall survival, analysed by use of flexible proportional mortality models, and we predicted survival under scenarios of modified distributions of risk factors.

Findings: Between Sept 8, 2014, and Dec 31, 2017, 2313 women were recruited from these eight hospitals, of whom 85 did not have breast cancer. Of the remaining 2228 women with breast cancer, 58 women with previous treatment or recurrence, and 14 women from small racial groups (white and Asian women in South Africa), were excluded. Of the 2156 women analysed, 1840 (85%) were histologically confirmed, 129 (6%) were cytologically confirmed, and 187 (9%) were clinically confirmed to have breast cancer. 2156 (97%) women were followed up for up to 3 years or up to Jan 1, 2019, whichever was earlier. Up to this date, 879 (41%) of these women had died, 1118 (52%) were alive, and 159 (7%) were censored early. 3-year overall survival was 50% (95% CI 48-53), but we observed variations in 3-year survival between different races in Namibia (from 90% in white women to 56% in Black women) and in South Africa (from 76% in mixed-race women to 59% in Black women), and between different countries (44-47% in Uganda and Zambia vs 36% in Nigeria). 215 (10%) of all women had died within 6 months of diagnosis, but 3-year overall survival remained low in women who survived to this timepoint (58%). Among survival determinants, improvements in early diagnosis and treatment were predicted to contribute to the largest increases in survival, with a combined absolute increase in survival of up to 22% in Nigeria, Zambia, and Uganda, when compared with the contributions of other factors (such as HIV or aggressive subtypes).

Interpretation: Large variations in breast cancer survival in sub-Saharan African countries indicate that improvements are possible. At least a third of the projected 416 000 breast cancer deaths that will occur in this region in the next decade could be prevented through achievable downstaging and improvements in treatment. Improving survival in socially disadvantaged women warrants special attention.

Funding: Susan G Komen and the International Agency for Research on Cancer.

Figure 1

Crude overall survival to 3 years after breast cancer diagnosis Kaplan-Meier survival curves showing crude 3-year overall survival in 2156 women by country and race or setting (A), and by stage at diagnosis (B). Kaplan-Meier survival curves showing crude 3-year overall survival in 1934 women who survived for 6 months or longer, by country and race or setting (C) and stage at diagnosis (D). HRs (95% CIs) in (A) and (C) show the comparison with Namibian white women, and HRs (95% CIs) show the comparison with stage IIA cancer at diagnosis. HR=hazard ratio.

Figure 2

Age-stage adjusted HRs for 3-year all-cause mortality in all 2156 women, by age, tumour characteristics, HIV status, and sociodemographic characteristics HR=hazard ratio. Hormone receptor-positive=oestrogen receptor-positive or progesterone receptor-positive. Hormone receptor-negative=oestrogen receptor-negative and progesterone receptor-negative. HER2=human epidermal growth factor Receptor 2. *In all countries except South Africa.

Figure 3

Observed and predicted 3-year survival from diagnosis (A) and conditional on surviving to 6 months (B) at the observed distribution of prognostic factors, and under specified improved scenarios, by site and race, and in public hospitals only Above the bar showing observed 3-year survival is the predicted survival of women if the following specified added improvements had been made: (1) downstaging to a stage at diagnosis distribution of 35% at stage I or IIA, 25% at stage IIB, 15% at stage IIIA, 10% at stage IIIB, 7% at stage IIIC, and 8% at stage IV, or in Namibian white and mixed-race women, in whom this distribution is already achieved, downstaging to a stage at diagnosis distribution of 60% at stage I or IIA, 20% at stage IIB, 5% at stage IIIA, 5% at stage IIIB, 5% at stage IIIC, and 5% at stage IV; (2) improving treatment, whereby all women receive surgery and systemic therapy; (3) reducing survival deficits associated with social inequalities (measured by level of education), whereby, for a given site-race group, women in each of the three education categories (none, primary, and secondary) have the same survival as that of women in the category above; (4) eliminating survival deficits associated with a HIV-positive status (5) eliminating survival deficits associated with being aged younger than 30 years; and (6) eliminating survival deficits associated with not having hormone receptor-positive, HER2-negative tumours. Survival model fits are provided in the appendix (p 10). HR=hazard ratio. HER2=human epidermal growth factor Receptor 2. Hormone receptor-positive=oestrogen receptor positive or progesterone receptor-positive.