Oral Diabetes Drugs May Improve Survival In Diabetics With Colorectal Cancer

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A common problem among diabetic patients is adherence to medications.  A new study has found that colorectal cancer patients who are compliant in taking oral diabetes drugs fare better than those who do not.

The study was published in Cancer Epidemiology, Biomarkers & Prevention a journal of the American Association for Cancer Research.

The association between diabetes and increased incidence of colorectal cancer is well established, explained Sunho Choe. Further, one of the paper’s authors.  The use of the antidiabetic medication metformin has been repeatedly shown to improve colorectal cancer survival among those with diabetes, he said. "However, it is estimated that the majority of patients take additional antidiabetic medications along with metformin, and how the combination of these medications affects the prognosis of colorectal cancer remains underexplored," he added.

In their retrospective cohort study, the researchers used information from the National Health Information Database in Korea, from 2002 to 2016. Individuals who had diabetes and were diagnosed with colorectal cancer in this time frame were included in the study, resulting in a total study population of 33,841 participants. Patients were followed for an average of 4.7 years.

The researchers used prescription data to calculate the patients' proportion of days covered (PDC), which is defined as the number of days with medications on hand divided by the number of days in a specified time interval to estimate patients' adherence to their oral antidiabetic medications. Adherence to prescribed injectable medications, including insulin, was not measured. The researchers categorized oral medication adherence into two groups for comparison: patients with high adherence had a PDC of at least 80 percent, while patients with low adherence had a PDC of less than 80 percent.

The researchers found that over 80 percent of patients were taking more than one oral antidiabetic medication and fewer than 23 percent of patients were in the high-adherence category. Compared to patients with high adherence, those with low adherence to their oral antidiabetic medication had a nearly 20 percent increase in their risk of overall mortality, in both crude and adjusted models.

High adherence to oral antidiabetic medication was found to have a protective effect for all colorectal cancer subgroups, with the most pronounced effect observed among patients with distal colon cancer.

"Based on our data, less than 25 percent of patients were taking their diabetes medications as prescribed, suggesting that over 75 percent of diabetic patients with colorectal cancer could benefit by adhering to these prescriptions," said Senior author Aesun Shin.

The researchers did not have access to some clinical information, including cancer stage, which is an important factor in comparing prognoses between different groups. In lieu of cancer stage, the researchers stratified the study population based on type of cancer treatment received. Patients who had early-stage disease likely received surgery alone, while patients with late-stage disease likely received palliative therapy, such as chemotherapy or radiotherapy without surgery.

Choe S, Lee J, Park JW, et al. Prognosis of Patients with Colorectal Cancer with Diabetes According to Medication Adherence: A Population-Based Cohort Study. Cancer Epidemiol Biomarkers Prev. 2020;29(6):1120‐1127. doi:10.1158/1055-9965.EPI-19-1455