There have been conflicting studies on whether Black women have denser breasts than women of other races. One study  indicated they do not, while a more recent study  indicated they do.
1. del Carmen MG, Halpern EF, Kopans DB, et al. Mammographic breast density and race. AJR Am J Roentgenol 2007; 188:1147-1150
2. McCarthy AM, Keller BM, Pantalone LM, et al. Racial differences in quantitative measures of area and volumetric breast density. J Natl Cancer Inst 2016; 108