Treatment and outcomes in diabetic breast cancer patients

Effective breast cancer management is more complex with diabetes present and may contribute to poor outcomes. Therefore, we conducted two simultaneous systematic reviews to address the association of diabetes with (1) treatment patterns in breast cancer patients and (2) breast cancer recurrence rates or breast cancer-specific and all-cause mortality. We searched major databases for English language peer-reviewed studies through November 2013, which addressed either of the above research questions, following the preferred reporting items for systematic reviews and meta-analyses (PRISMA) method. Analyses compared treatment patterns or health outcomes for breast cancer subjects with and without diabetes. We used STROBE quality criteria and conducted a random-effects meta-analysis of all-cause mortality. The review yielded 11 publications for question 1 and 26 for question 2, with nine overlapping. Treatment studies showed chemotherapy was less likely in patients with diabetes. Of 22 studies, 21 assessing all-cause mortality indicated a statistically significant increased overall mortality for patients with diabetes (hazard ratios: 0.33–5.40), with meta-analysis of eligible studies indicating a 52 % increased risk. Nine studies assessing breast cancer-specific mortality had inconsistent results, with five showing significantly increased risk for diabetes patients. Results were inconsistent for recurrence and metastases. The majority of studies reported detrimental associations between diabetes and optimal treatment or all-cause mortality among women with breast cancer. Divergence in variable and outcomes inclusion and definitions, potential participation bias in individual studies, and differing analytic methods make inferences difficult. This review illuminates the importance of the impact of diabetes on breast cancer patients and explicitly recognizes that co-management of conditions is necessary to prevent excess morbidity and mortality.