The presence of type 2 diabetes mellitus at the time of breast cancer diagnosis has been suggested to adversely affect survival—independent of breast cancer stage, grade, and tumor phenotype—but few of those studies included people of Hispanic descent. Researchers from Johns Hopkins Bloomberg School of Public Health in Baltimore and the University of Louisville in Kentucky examined the association between self-reported diabetes history, breast cancer-specific and all-cause mortality among Hispanic and non-Hispanic white women diagnosed with breast cancer. They presented their results on Saturday, December 9, during a poster session at the San Antonio Breast Cancer Symposium.
The researchers analyzed data from a total of 399 patients (96 Hispanic and 303 non-Hispanic white women) with stages I–IIIa breast cancer from the New Mexico Health, Eating, Activity, and Lifestyle cohort who were diagnosed with breast cancer between July 1996 and March 1999.
In total, 134 deaths occurred; the median follow-up time was 13.5 years from baseline interview to death. The prevalence of diabetes did not differ significantly by ethnicity; 11.5% of Hispanics reported having diabetes compared to 7.5% of non-Hispanic white women.
Hazard ratios (HR) and 95% confidence intervals (CI) were calculated using multivariable Cox proportional hazards regression models. Although a history of diabetes was associated with older age at breast cancer diagnosis (p = 0.001), higher body fat percentage (p = 0.01), higher body mass index (p < 0.001), and increased waist-to-hip ratio (p < 0.001) compared to non-diabetics, no significant differences were observed between diabetics and non-diabetics for breast cancer stage, grade, tumor phenotype, or receipt of breast cancer treatment.
In multivariable models, diabetes was associated with increased risk of all-cause mortality overall (HR = 2.10, 95% CI = 1.24–3.55), with a significant association only observed among Hispanic women (HR = 3.07, 95% CI = 1.05–8.94) when compared to non-Hispanic white women (HR = 1.66, 95% CI = 0.86–3.24).
The interaction between ethnicity and diabetes was not statistically significant for all-cause mortality. Diabetes also was significantly associated with increased risk of breast cancer-specific mortality (HR = 2.89, 95% CI = 1.27–6.60); however, results were not statistically significant by ethnicity.