NIV Congres

Introduction: In developed countries, 40% of breast cancer patients is older than 65 years of age at diagnosis and this percentage is increasing. Elderly breast cancer patients differ significantly from younger patients, since high age is predictive for comorbidity and decreased functioning. Up to 16% of elderly breast cancer patients suffer from diabetes. In several cohort studies, it has been shown that diabetes increases both overall and breast cancer specific mortality.

Aim of the study: The aim of this study was to assess the impact of diabetes in combination with other comorbidities on overall mortality in elderly breast cancer patients.

Materials and Methods: Patients were selected from the FOCUS cohort study which contains detailed information on all consecutive patients aged 65 years and older with breast cancer diagnosed between 1997 and2004 inthe South-West part of the Netherlands.

For this study, patients with stage 0-III breast cancer who received surgical treatment were selected. Patients were divided into four groups: no comorbidity, diabetes only, diabetes with other comorbidity and other comorbidity only. Survival analyses with Kaplan Meier and Cox Regression models were performed.

Results: Overall, 3003 patients were selected, of whom 492 (16.4%) were diagnosed with diabetes. In Kaplan Meier analyses, patients with diabetes without other comorbidity had a significantly better overall survival than patients without comorbidity, patients with diabetes and other comorbidity, or other comorbidity (without diabetes) (p < 0.001). In a Cox regression model adjusted for age, tumour and treatment characteristics, patients with diabetes only had a non-significant better overall survival than patients without comorbidity (HR 0.82; 95% CI 0.52-1.30), while patients with diabetes and other comorbidity had a significantly worse overall survival (HR 1.65; 95% CI 1.39-1.96). After stratification by age and hormone receptor sensitivity, similar results were observed.

Conclusion: Overall survival in elderly breast cancer patients with diabetes only was similar to survival of patients without comorbidity. However, both patients with diabetes and other comorbidity and patients with other comorbidity without diabetes had a significantly worse overall survival. A possible explanation for the survival benefit of patients with diabetes without other comorbidity might be the use of metformin since it has been shown in several large cohort studies that metformin provides a survival benefit in cancer. Prospective studies should address the effectiveness of metformin as adjuvant treatment in early breast cancer since the paucity of side effects makes metformin an attractive adjuvant agent in elderly patients.