Abstract A40: Body size and racial/ethnic differences in breast cancer survival.
Authors: Kwan Marilyn L. , Caan Bette J. , Lee Valerie S. , John Esther M. , Gomez Scarlett Lin , Shariff-Marco Salma , Keegan Theresa H. , Kurian Allison W. , Bernstein Leslie , Lu Yani , Cheng Iona , Monroe Kristine R. , Sposto Richard , Vigen Cheryl , Wu Anna H. 
Published: August 2014

Background: Studies of body size and breast cancer prognosis have primarily been conducted in non-Latina White women with little research to date in racial/ethnic minority groups. We investigated body size (body mass index [BMI], waist-hip-ratio [WHR], waist-height-ratio [WHtR], waist circumference [WC]) and survival by race/ethnicity (non-Latina White, African American, Asian American, and Latina) in the California Breast Cancer Survivorship Consortium (CBCSC).

Methods: The CBCSC represents 12,025 breast cancer patients diagnosed with primary invasive breast cancer from 1993-2007 from six California-based studies of breast cancer etiology or prognosis. Data on body size, race/ethnicity, and relevant covariates previously collected from in-person interview or mailed questionnaire were harmonized and pooled. Clinical characteristics and mortality information were obtained from the California Cancer Registry. Body size measures included minimum 6 months pre-diagnosis BMI in kg/m2 (underweight &lt;18.5, normal 18.5-&lt;25, overweight 25-&lt;30, obese 30-&lt;35, severely obese 35-&lt;40, morbidly obese ≥40), and median 1 year post-diagnosis WHR, WHtR, and WC (quartiles). Cox proportional hazards models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for the associations of each body size measure with all-cause and breast cancer-specific (BC) mortality, adjusted for sociodemographic, lifestyle, clinical, and treatment covariates.

Results: Among 11,351 women with BMI data (6,044 non-Latina Whites, 1,886 African Americans, 1,451 Asian Americans, 1,864 Latinas, and 106 others), a total of 2,744 deaths (1,445 BC-related) were observed after a mean (SD) follow-up of 11.0 (3.8) years. Underweight and morbidly obese women had a statistically significant increased risk of overall mortality compared to normal-weight women (underweight HR=1.47; 95% CI: 1.13, 1.90 and morbidly obese HR=1.43; 95% CI: 1.16, 1.77; p for trend=0.012; departure from linearity p=0.005) while obese and severely obese women had borderline significant increased risks. Similar yet attenuated associations were found for BC mortality. Women in the highest WHR quartile compared to those in the lowest quartile had a significant increased risk of both overall death (HR=1.30; 95% CI: 1.10, 1.55) and BC death (HR=1.36; 95% CI: 1.07, 1.73) with a positive trend of larger WHR and increasing risk (p for trend&lt;0.05). WHtR and WC had similar associations with mortality as WHR. Compared to the entire cohort, non-Latina Whites had an analogous U-shaped association of BMI with mortality risk, while African Americans and Asian Americans had no associations at any BMI level. Latinas had elevated risks only among the morbidly obese. In contrast, larger WHR was associated with mortality in African Americans (p for trend&lt;0.001) while no associations with WHR were found in non-Latina Whites. Asian Americans had elevated risks only in the top WHR quartile. WHtR and WC were not associated with mortality in any race/ethnicity group.

Conclusion: In this large, multiethnic study of breast cancer patients, we found that those with extreme BMI and increased WHR had the worse survival but that the associations varied by race/ethnicity. Obesity and body fat distribution around breast cancer diagnosis appear to have differential effects on survival depending on race/ethnicity.

Funded by the California Breast Cancer Research Program

Citation Format: Marilyn L. Kwan, Bette J. Caan, Valerie S. Lee, Esther M. John, Scarlett Lin Gomez, Salma Shariff-Marco, Theresa H. Keegan, Allison W. Kurian, Leslie Bernstein, Yani Lu, Iona Cheng, Kristine R. Monroe, Richard Sposto, Cheryl Vigen, Anna H. Wu. Body size and racial/ethnic differences in breast cancer survival. [abstract]. In: Proceedings of the Fifth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2012 Oct 27-30; San Diego, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2012;21(10 Suppl):Abstract nr A40.