Background: Racial disparities in breast cancer outcomes pose a major public health challenge. Complex interactions between social determinants of health and tumor biology, mediated by obesity and adiposity, may play an important role in these disparities. White adipose tissue inflammation (WATi) of the breast, which is histologically defined by the presence of crown-like structures (CLS-B), occurs in the setting of excess adiposity and promotes tumor growth via elevated levels of aromatase, proinflammatory growth factors, and metabolic dysregulation. Here we examined relationships between race, body mass index (BMI), and WATi in two cohorts of patients with early-stage breast cancer: 1) American Black women and 2) indigenous Nigerian women. Methods: Non-tumor breast WAT specimens were collected from patients undergoing mastectomy for treatment or prevention of breast cancer at Memorial Sloan Kettering Cancer Center (MSK) in the US and Obafemi Awolowo University Teaching Hospital (OAUTH) in Nigeria. WATi was defined by the presence of CLS-B as detected by CD68 immunostaining. All tissue analyses were performed at MSK. Associations among BMI and WATi were tested within each cohort using Kendall’s tau rank correlation and compared between cohorts using Pearson's Chi-squared test. Results: A total of 224 American women were enrolled at MSK between 2011-2018, of whom 39 self-reported Black race. At OAUTH, 97 Nigerian women were enrolled between 2018-2022. Invasive carcinoma was present in 32 American Blacks and 97 Nigerians. Of those with invasive carcinoma, the prevalence of WATi among American Black women was 72% vs. 37% in the Nigerian cohort (p<0.001). In the US cohort, there was no significant difference between the prevalence of WATi among Black vs. non-Black patients (72% vs. 62%; p=0.3). 44% of American Blacks were obese and 34% overweight compared with 27% and 39% of Nigerians, respectively (p=0.07). The prevalence of WATi varied by BMI category within each cohort, as shown. Overweight/obesity was associated with WATi in the Nigerian (p=0.009) and American cohorts (p<0.001); a trend was observed in the American Black subgroup (p=0.13). Conclusions: Breast WATi and obesity were more prevalent among American Black women with breast cancer compared with Nigerian women. These findings highlight the need for further investigation of environment, lifestyle patterns, and body composition differences between indigenous and diaspora populations.

¹Kendall’s rank correlation tau.