Background: Despite the lack of scientific data, many cancer patients hold the belief that glucose 'feeds' cancer and might affect disease outcome. We aimed to evaluate associations between glucose, hemoglobin A1C (HbA1C), and survival among individuals with diabetes and diabetes associated cancers.
Methods: Five retrospective cohort studies were conducted in a large population-representative database. The study population included all patients with diabetes and an incident diagnosis of colorectal, breast, bladder, pancreatic and prostate cancers. Exposure of interest was serum glucose or HbA1C levels within 6 months prior to cancer diagnosis. Cox regression model was used to calculate hazard-ratio (HR) and 95% confidence-interval (CI) for overall survival. Analyses were adjusted for cancer-specific confounders. A subgroup analysis was performed among insulin-treated patients.
Results: Study cohorts included 7916 individuals with incident cancers and concurrent diabetes. There was no association between HbA1C levels and overall survival in colorectal (HR 1.00, 95% CI 0.95-1.06), breast (HR 1.03, 95% CI 0.95-1.11), bladder (HR 0.94, 95% CI 0.86-1.01), pancreatic (HR 0.98, 95% CI 0.94-1.02), or prostate (HR 1.02, 95% CI 0.96-1.08) cancers. Among diabetes patients treated with insulin, there was increased survival with increasing serum glucose, most prominent for bladder cancer (HR 0.91, 95% CI 0.84-0.99, per 1 mmol/l increase).
Conclusions: Higher glucose and HbA1C levels in diabetes patients with incident cancer are not associated with worse overall survival following cancer diagnosis. Among insulin-treated patients, higher glucose levels may be associated with improved survival.
Keywords: Cancer; Diabetes; Glucose; HbA1C; Insulin; Survival.
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