Background
Breast cancer (BC) is the most common female cancer in sub-Saharan Africa (SSA), with incidence expected to rise markedly in the next decades due to demographic changes and rises in the prevalence of risk factors - a rise that is inevitable as there are few preventive measures. BC is, however, curable if diagnosed at an early-stage and managed with multi-modal treatments. Previous estimates in SSA, most of limited quality, indicated that survival from BC in the region is much lower than in high-income countries.
 
Objectives
The ABC-DO cohort is a multi-dimensional study that aims to dissect for the first time the entire BC journey, from symptom recognition to diagnosis, treatment and survivorship, to identify proximal and distal enablers and barriers to early diagnosis, treatment uptake and completion, survivorship and, ultimately, survival in the region.
 
Methods
Over 2200 women aged ≥18 years with a BC newly-diagnosed between Sept-2014 and Sept-2017 were recruited in eight hospitals in five SSA countries (Namibia, Uganda, Nigeria, Zambia and South Africa) chosen to represent different BC epidemiological transitions, socio-economic levels and healthcare systems. This cohort was followed trimonthly for over 7 years to allow in-depth examination of long-term survival and survivorship after a BC diagnosis, and investigation of their socio-demographic, geospatial, clinical and biological determinants. The study was implemented via a specifically-tailored m-Health application to facilitate study management, ensure collection of high-quality standardised data, and minimize losses to follow-up (a critical flaw of previous survival studies in SSA).
 
Results
Major findings include marked disparities in survival after a BC diagnosis with Black African women (5-year age-standardised net survival: 35–42% in Zambia and Nigeria, 52–58% in Black women in Uganda, South Africa and Namibia) having much poorer survival than mixed race and White women in Namibia (>84%). Advanced stage at diagnosis and poor access to surgery and systemic therapy, which affected particularly women from lower socioeconomic groups and those who resided far away from oncological centres, were the largest contributors to the low survival whilst the relatively high proportion of young-onset BC (<30 years at diagnosis), high proportion of HIV-affected women, and high frequency of more aggressive tumour subtypes making much smaller contributions. Ensuring that 60% patients are diagnosed at an early stage (TNM I/II) and have access to effective treatment would lead to about one-third reduction in deaths amongst Black women. The ABC-DO has also revealed the wide intergenerational impact of BC deaths in SSA, with half of the deaths occurring in women aged <50 years, each of whom left behind, on average, two maternal orphans (children aged <18 years).
 
Conclusions/Implications
The ABC-DO study demonstrates how well-conducted international studies can inform  cancer control policies, with its findings having informed the WHO Global Breast Cancer Initiative aims and pillars of action, by pointing to the need to reduce mortality from BC through effective strategies for downstaging the disease via improvements in women’s BC awareness and timely diagnosis, and for ensuring access to, and compliance with, high-quality treatment.