BACKGROUND: With increasing prevalence of type 2 diabetes, it has become one of the common comorbidities among breast cancer patients. Few contemporary studies have examined the effect of preexisting diabetes on survival outcomes in breast cancer patients. Furthermore, both breast cancer mortality and diabetes prevalence are higher in African American women compared to Caucasian women, yet data on whether diabetes can explain racial disparity in breast cancer mortality is scarce.

OBJECTIVE: To compare clinopathological characteristics and survival outcomes between breast cancer patients with and without co-existing diabetes, and to explore the contribution of diabetes to breast cancer survival differences between African Americans and Caucasians.

METHODS: We analyzed data from the Chicago Multiethnic Epidemiologic Breast Cancer Cohort (ChiMEC) comprising of 3170 histologically confirmed breast cancer patients diagnosed between 2004 and 2017. The cohort consists of 55% Caucasians, 38% African Americans, and 7% other ethnicities. Cox models were used to analyze data on several clinical outcomes.

Table 1

  Unadjusted HR (95% CI) p Adjusted HR (95% CI)* p 
All-cause mortality 2.20 (1.65-2.92) <0.001 1.79 (1.33-2.43 <0.001 
Breast Cancer-specific mortality 1.61 (1.06-2.44) 0.025 1.97 (1.27-3.05) 0.002 
Non-breast cancer mortality 3.14 (2.11-4.69) <0.001 1.62 (1.06-2.47) 0.025 
Time to recurrence 1.18 (0.76-1.85) 0.46 1.41 (0.89-2.25) 0.15 
Recurrence-free survival 1.73 (1.32-2.26) <0.001 1.68 (1.27-2.22) <0.001 
  Unadjusted HR (95% CI) p Adjusted HR (95% CI)* p 
All-cause mortality 2.20 (1.65-2.92) <0.001 1.79 (1.33-2.43 <0.001 
Breast Cancer-specific mortality 1.61 (1.06-2.44) 0.025 1.97 (1.27-3.05) 0.002 
Non-breast cancer mortality 3.14 (2.11-4.69) <0.001 1.62 (1.06-2.47) 0.025 
Time to recurrence 1.18 (0.76-1.85) 0.46 1.41 (0.89-2.25) 0.15 
Recurrence-free survival 1.73 (1.32-2.26) <0.001 1.68 (1.27-2.22) <0.001 

*Adjusted for age, race, stage, hormone therapy, and chemotherapy

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RESULTS: 245 patients (8%) in the cohort had co-existing diabetes at time of breast cancer diagnosis, with African Americans having highest prevalence (14%). Patients with diabetes were older (mean 66 vs. 56 years old) and had higher proportion of obesity (67% vs. 34%) and Charlson comorbidity index >2 (27% vs. 10%) than those without diabetes. The two groups were similar in terms of surgery, radiation, and hormonal therapy received, while patients with diabetes had slightly more advanced stage (15% vs. 10%). After adjusting for multiple prognostic factors, patients with diabetes had a 97% higher risk of dying from breast cancer and a 62% fold higher risk dying from other causes than patients without diabetes (Table). The two groups had no significant difference in risk of recurrence. In addition, the hazard ratio (HR) comparing African Americans with Caucasians was 2.35 (95% confidence interval [CI] 1.90-2.91), and it changed to 2.19 (95% CI 1.76-2.33) after the adjustment for diabetes.

CONCLUSIONS: Pre-existing diabetes among breast cancer patients was associated with higher risk of breast cancer specific and all-cause mortality. About 11% of racial disparities in breast cancer mortality could be attributed to higher difference in diabetes prevalence in African American patients. Further research investigating how pre-existing diabetes may influence breast cancer treatment and survival are warranted.

Citation Format: Neerukonda AR, Olopade OI, Huang E, Huo D. Type 2 diabetes and survival outcomes among a multi-ethnic cohort of breast cancer patients [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-08-05.

©2019 American Association for Cancer Research.
2019
American Association for Cancer Research.