Abstract
PurposePreexisting diabetes is associated with increased morbidity and mortality in cancer. We examined the impact of incident cancer on the long-term outcomes of diabetes.MethodsUsing the United Kingdom Clinical Practice Research Datalink, we identified three cohorts of diabetes patients subsequently diagnosed with breast, colorectal, or prostate cancer, each matched to diabetic noncancer controls. Patients were required to have survived at least 1 year after cancer diagnosis (cases) or a matched index date (controls), and were followed up to 10 years for incident microvascular and macrovascular complications and mortality. Multivariate competing risks regression analyses were used to compare outcomes between cancer patients and controls.ResultsOverall, there were 3382 cancer patients and 11,135 controls with 59,431 person-years of follow-up. In adjusted analyses, there were no statistically significant (p ≤ 0.05) differences in diabetes complication rates between cancer patients and their controls in any of the three cancer cohorts. Combined, cancer patients were less likely (adjusted hazard ratio [HR] 0.88; 95% CI = 0.79–0.98) to develop retinopathy. Cancer patients were more likely to die of any cause (including cancer), but prostate cancer patients were less likely to die of causes associated with diabetes (HR 0.61; 95% CI = 0.43–0.88).Conclusions and implicationsThere is no evidence that incident cancer had an adverse impact on the long-term outcomes of preexisting diabetes.Implications for Cancer SurvivorsThese findings are important for cancer survivors with preexisting diabetes because they suggest that substantial improvements in the relative survival of several of the most common types of cancer are not undermined by excess diabetes morbidity and mortality.
Highlights
Cancer patients were more likely to die of any cause, but prostate cancer patients were less likely to die of causes associated with diabetes (HR 0.61; 95% CI = 0.43–0.88)
There is no evidence that incident cancer had an adverse impact on the long-term outcomes of preexisting diabetes
Implications for Cancer Survivors These findings are important for cancer survivors with preexisting diabetes because they suggest that substantial improvements in the relative survival of several of the most common types of cancer are not undermined by excess diabetes morbidity and mortality
Summary
Evidence from epidemiologic studies, as summarized in a number of recent reviews [1,2,3,4,5,6,7,8,9,10], indicates that preexisting diabetes is associated with worse short- and long-term outcomes of cancer, both overall [9, 10] and in specific types of cancer including breast [3, 4, 10], colorectal [2,3,4,5,6,7, 10], and prostate [8]. There is considerably less information on how cancer impacts the long-term outcomes of preexisting diabetes [12, 20]. As early detection and advances in cancer therapy and supportive care have substantially improved the relative survival of many of the most common types of cancer [21], overall morbidity and mortality in cancer depend increasingly on the quality and outcomes of primary care for other underlying conditions [22]. Cancer organizations, such as Cancer Research UK and Macmillan Cancer Support in the United Kingdom (UK), have expressed concern that overlooking other medical conditions during cancer treatment and follow-up could result in excess morbidity and mortality, thereby undermining gains associated with early detection and treatment of cancer [23, 24]
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