Cancer
Beyond BMI: racial and ethnic variation of body size and body composition in individuals with stage II and III breast cancer Ijeamaka Anyene Fumagalli* Ijeamaka Anyene Fumagalli Erica T. Warner Adana Llanos Elizabeth Cespedes Feliciano
Background:
While a common proxy for adiposity, body mass index (BMI) cannot distinguish muscle from adipose tissue and thus may not reflect associations of adiposity with disease outcomes. We examined racial and ethnic differences in body composition among breast cancer patients and associations of multiple physiologically relevant measures of adiposity with survival.
Methods:
We included 3,898 women diagnosed with stage II-III breast cancer from 2005-2019 at Kaiser Permanente with CT scans from which we derived mid-L3 area of skeletal muscle (SKM), subcutaneous (SAT), visceral (VAT), and intermuscular (IMAT) adipose tissue. Adjusting for age at diagnosis, we examined body composition distributions among Asian/Pacific Islander (API) (N=754), Non-Hispanic (NH) Black (NHB) (N=331), Hispanic (N=534), and NH-white (N=2279) women. We then fit Cox proportional hazard models to estimate hazard ratios and 95% confidence intervals for the associations of body composition with survival within strata of BMI and race/ethnicity.
Results:
API women had the lowest mean BMI (mean±SD, 26±9) and NHB women had the highest mean BMI (32±7). Adjusting for age at diagnosis and BMI, NHB women with higher BMI had higher SAT (eg, BMI 30-<35 kg/m2: 337 [NHB] vs 300 [API], 322 [HISP], 319.4 [NHW]) and SKM (eg, BMI 30-<35 kg/m2: 129 [NHB] vs 116 [API], 118 [HISP], 122 [NHW]) but lower VAT (eg, BMI 30-<35 kg/m2: 118 [NHB] vs 146 [API], 151 [HISP], 156 [NHW]) area in cm2 than other groups. Over a median follow-up of 6.8 years, 742 breast cancer deaths occurred. Associations of each tissue with breast-cancer mortality varied by race/ethnicity and BMI with the most consistent associations for greater risk with increasing VAT among NHB and API women, but confidence intervals were imprecise.
Conclusion:
BMI obscures differences in body composition by race and ethnicity. Examining adipose tissue distribution within strata of BMI reveals differing associations within and amongst racial and ethnic groups.
