Abstract
Purpose: Meta-analyses of the association between diabetes and postmenopausal breast cancer have been conducted primarily among white women with summary relative risks [RR] of approximately 1.15 (95% confidence interval (CI) 1.07-1.24). The only related prospective cohort study among black women reported a RR of 0.93 (95% CI 0.73-1.19). We conducted a case-control study to examine whether diabetes was associated with subsequent breast cancer among postmenopausal black women and whether obesity modified this association.
Methods: Women diagnosed with incident postmenopausal breast cancer between September 2009 and December 2012 were identified through statewide cancer registries in Georgia, South Carolina and Tennessee. One control per case, individually matched on age at enrollment, state and household income, were selected from Southern Community Cohort Study participants. Women whose breast cancer and diabetes were diagnosed within one year of each other were excluded to minimize detection bias resulting in 839 cases and 839 controls for analysis. Data on diabetes (cases n=244, controls n=336) and obesity (cases n=468, controls n=466) were obtained from baseline surveys; data on breast cancer histologic subtype (estrogen receptor (ER) positive n=556, ER negative n=216) were from cancer registry records.
Results: Using conditional logistic regression with further adjustment for educational level and health insurance coverage, there was a reduced risk of breast cancer associated with self-reported diabetes (odds ratio (OR) 0.63, 95% CI 0.49-0.80). Obesity did not significantly modify the effect of diabetes on breast cancer, but there was a stronger risk reduction among non-obese women (OR 0.51, 95% CI 0.34-0.77) than obese women (OR 0.69, 95% CI 0.50-0.94) (p for interaction=0.25). The inverse association was more pronounced for ER positive breast cancer (OR 0.51, 95% CI 0.37-0.70) than ER negative breast cancer (OR 0.84, 95% CI 0.51-1.37). However, the difference was not statistically significant.
Conclusions: In this large case-control study among black women, we found the first evidence suggesting a significant inverse association between diabetes and postmenopausal breast cancer risk. Future studies are needed to confirm our findings and to evaluate the underlying mechanisms, particularly regarding metformin use.
Citation Format: Maureen Sanderson, Loren Lipworth, David Shen-Miller, Martha J. Shrubsole, Alicia Beeghly-Fadiel, Sarah Nechuta, Xiao-ou Shu, Wei Zheng. Interaction of diabetes and obesity in postmenopausal breast cancer risk among black women. [abstract]. In: Proceedings of the Eighth AACR Conference on The Science of Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; Nov 13-16, 2015; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2016;25(3 Suppl):Abstract nr A58.
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