Differences in breast cancer incidence and mortality rates between North American Caucasian and African American women are well-described and transcend socioeconomic issues. Black women are diagnosed with breast cancer at a younger median age; have more clinically aggressive disease and stage-for-stage; and have higher mortality rates than age-matched Caucasian women. Black women in West Africa, the origin of the slave trade in the US in the 19th century and thus the founder population for most African Americans, have even higher rates of early-onset, poor-prognosis breast cancer than African American women. Racial difference in the distribution of intrinsic molecular subtypes has been well characterized in the US and throughout the African Diaspora as well. Despite the large efforts on characterizing racial/ethnic differences, however, the reasons women of African ancestry are disproportionately affected by breast cancer incidence and mortality remain poorly understood - largely due to paucity of data on inherent genomic differences that contribute to the disparities in incidence and progression of breast cancer across populations. West Africa Breast Cancer Study (WABCS) is an initiative that aims to comprehensively understand the genetic architecture of breast cancer in West Africans, the founder population of a large proportion of black women in the United States. The objective of the study was to provide a better understanding of the molecular genetic factors that influence prognosis in Nigerian breast cancer patients, and determine which of these alterations may be amenable to available therapy. To that end, we examined the molecular features of breast cancers of indigenous African women using a combination of whole-genome, whole-exome, and transcriptome sequencing (WGS, WES, and RNA-seq) on 194 tumors from Nigerian patients. The goal of this project was to obtain answers to two related research questions using an unscreened population without genetic admixture in Nigeria: 1) why are women of African ancestry more likely to develop aggressive young onset breast cancer? 2) What are the associated genomic and non-genomic risk factors? We hypothesize that the genomic determinants of breast cancer molecular subtypes in women of African ancestry are also molecular drivers of tumor progression and represent targets for interventions to improve clinical outcomes and close the mortality gap. By identifying causal links between genetic variants that promote aggressive tumor progression in Nigerian women in comparison to women from different population found in TCGA and ICGC, the present dataset will have significant public health impact on millions of women in the African Diaspora. The potential to identify novel pathways for interventions to reduce the increasing mortality gap between women of African and European ancestry is huge