Racial and ethnic variation in body composition and prognosis of nonmetastatic breast cancer

Abstract Background The disproportionate burden of obesity among Black women may contribute to disparities in breast cancer survival; yet, associations of body mass index (BMI), a proxy for total adiposity, are inconsistent. Methods To examine racial/ethnic differences in body composition and evaluate associations with breast cancer–specific and all‐cause mortality, this study identified 3898 women 18 to <90 years old, diagnosed in 2005–2019 with stage II‐III breast cancer at Kaiser Permanente Northern California. The authors measured subcutaneous, visceral, and intermuscular adipose tissue area from computed tomography scans. Results Body composition differed by race: compared to other race/ethnicity groups, Black women had higher skeletal muscle and subcutaneous adipose, but lower visceral adipose tissues, whereas Asian/Pacific Islander women had lower intermuscular and subcutaneous adipose tissue. BMI was not significantly associated with mortality in any group. Among Black women, higher subcutaneous adipose tissue was associated with breast cancer–specific mortality (hazard ratio [HR], 1.24; 95% confidence interval [CI], 1.02–1.52) and all adipose tissue measures were associated with increased all‐cause mortality (intermuscular HR, 1.26; 95% CI, 1.09–1.46; subcutaneous HR, 1.25; 95% CI, 1.05–1.48; and visceral HR, 1.32; 95% CI, 1.03–1.68, respectively). By contrast, only increased intermuscular adipose tissue was associated with all‐cause mortality among White women (HR, 1.08; 95% CI, 1.00–1.16), with null associations for Hispanic and Asian/Pacific Islander women. Conclusions BMI obscures variation in body composition, particularly for Black women, who have more subcutaneous adipose and skeletal muscle but less visceral adipose tissue at higher BMIs. These findings from routine imaging highlight opportunities for tailored lifestyle interventions to improve survivorship and mitigate disparities.