ESR1 and breast cancer: Studies of these markers in African women with breast cancer in sub-Saharan Africa (SSA) have had extremely variable findings; reported percentages of estrogen receptor negative (ERN) tumors range from 30% to 40% [3-5] to >70% [6-9]; in comparison, corresponding percentages in the United States are 35% in breast cancer patients aged 40 and decline to 15% to 20% by age 70, and are slightly higher in black than in white American women [10].