Does diabetes affect breast cancer survival?

The objective of this study is to investigate the influence of diabetes on breast cancer-specific survival among women with breast cancer in Aotearoa/New Zealand.

This study included women diagnosed with invasive breast cancer between 2005 and 2020, with their information documented in the Te Rēhita Mate Ūtaetae-Breast Cancer Foundation National Register. Breast cancer survival curves for women with diabetes and those without diabetes were generated using the Kaplan-Meier method. The hazard ratio (HR) of breast cancer-specific mortality for women with diabetes compared to women without diabetes was estimated using the Cox proportional hazards model.

For women with diabetes, the 5-year and 10-year of cancer-specific survival were 87% (95% CI: 85%-88%) and 79% (95% CI: 76%-81%) compared to 89% (95% CI: 89%-90%) and 84% (95% CI: 83%-85%) for women without diabetes. The HR of cancer-specific mortality for patients with diabetes compared to those without diabetes was 0.99 (95% CI: 0.89-1.11) after adjustment for patient demographics, tumor characteristics, and treatments. Age at cancer diagnosis and cancer stage had the biggest impact on the survival difference between the two groups. When stratified by cancer stage, the cancer-specific mortality between the two groups was similar.

While differences in survival have been identified for women with diabetes when compared to women without diabetes, these are attributable to age and the finding that women with diabetes tend to present with more advanced disease at diagnosis. We did not find any difference in survival between the two groups due to differences in treatment.