Protective factor against breast cancer in Black women?

Breast cancer incidence has been found to be higher in those with higher SES, and incidence is highest among Whites, followed by Blacks, then Asians and Hispanics. Using several previous studies, this study finds that the disparity in breast cancer risk between ethnic groups can be accounted for by differences in SES, except for the disparity between Blacks and others.

"In contrast, for the black population, seven of the eight
analyzed datasets showed no difference in the incidence
of breast cancer at highest level of SES compared to the
lowest level, with only one dataset demonstrating a statistically significant disparity (data set 1: IRR 1.39, lower limit of 95% CI=1.04). This suggests that, as opposed to the apparent contributory effect of high SES on breast cancer risk in white, Hispanic and Asian/Pacific-Islander women, the risk of breast cancer in black women may not be significantly modified by SES."

in the conclusion:

"As for black women, the overall lack of statistically significant incidence rate ratios in Table 1 suggests that SES effects do not play an important role in modifying the risk of breast cancer in this population. This suggestion is supported by Chlebowski’s analysis, in which adjustment for SES-correlated breast cancer risk factors failed to eliminate the differencein hazard ratio of between black women and women of other races. Taken together, these findings imply the presence of a protective factor, which is not modified by SES, against breast cancer in black women."

There's a brief mention at the end about the grade and aggressiveness of breast cancer among Black women.

Disparities in breast cancer incidence across racial/ethnic strata and socioeconomic status: a systematic review
Vainshtein J.
J Natl Med Assoc. 2008 Jul;100(7):833-9.

OBJECTIVES: A higher incidence of breast cancer has been reported both in white women and women of higher socioeconomic status (SES) compared to women of other races and lower SES, respectively. We explored whether differences in SES can account for disparities in breast cancer incidence between races. METHODS: We identified several studies published between 1990 and 2007 that addressed disparities in breast cancer incidence across racial and socioeconomic strata. For each study, we calculated incidence rate ratios (IRRs) for breast cancer incidence in the highest strata to lowest strata of SES for white, black, Hispanic and Asian/Pacific-Islander populations. We then used these IRRs to compare trends in SES and breast cancer incidence between races and across studies. RESULTS: The studies we identified revealed that the magnitude of the disparity in breast cancer incidence between races decreases with increasing SES. While individual census-tract based studies' methods of assessing the association between SES and breast cancer incidence did not identify consistent trends between races, adjustment for risk factors closely correlated with SES eliminated the statistical differences in breast cancer incidence between women of white, Hispanic and Asian/Pacific-Islander, but not black, ethnicity. CONCLUSION: We found that racial differences in breast cancer incidence can largely be accounted for by ethnic differences in SES among white, Hispanic and Asian/Pacific-Islander women, but not between these populations and black women. We further highlight important differences in methodology between previously published studies that may account for their disparate findings.