Prognosis of Patients with Colorectal Cancer with Diabetes According to Medication Adherence: A Population-Based Cohort Study.

ABSTRACT

BACKGROUND: Diabetes mellitus is known to have a negative effect on colorectal cancer survival due to hyperinsulinemia or hyperglycemia, and medications such as metformin, which targets insulin resistance and hyperinsulinemia, have a preventive effect on the risk of death. The aim of this study was to compare the risk of death among patients with colorectal cancer with diabetes with different levels of adherence to oral antidiabetics. METHODS: National Health Information Database was used, which has all claims data for those who are registered for national health insurance in Korea, from 2002 to 2016, for conducting a retrospective cohort study. Newly diagnosed patients with colorectal cancer among diabetics were followed up from the date of diagnosis until death or December 31, 2016. The medication adherence was calculated as the proportion of days covered (PDC). The HR and 95% confidence interval (CI) for death were estimated using the low-adherence patients as a reference. RESULTS: A total of 33,841 diabetic patients with newly diagnosed colorectal cancer were followed for an average of 4.7 years. Patients with colorectal cancer with good adherence (PDC ≥ 80%) showed a reduced risk of death [HR (95% CI), 0.82 (0.78-0.86)] compared with those with poor adherence (PDC < 80%). A reduced risk of death was observed for all cancer subsites. CONCLUSIONS: The maintenance of good medication adherence for diabetes mellitus was related to a favorable prognosis of colorectal cancer. IMPACT This study provides evidence that patients with colorectal cancer who are adherent to their diabetes medication will have better survival than patients who are not adherent.