Despite a high percentage of patients with diabetes prescribed multiple oral antidiabetic medications, investigators found that less than a quarter of study participants with colorectal cancer were taking their medications as prescribed, suggesting that many could benefit from improved adherence.

The association between diabetes and colorectal cancer has been established in earlier studies and the use of metformin has also been shown to improve survival rates among this population. Earlier studies have investigated this link, but the authors noted that research investigating survival rates and various levels of adherence is lacking.

“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,” said Sunho Choe, MD, first author of the study, in a statement.

The investigators used data from the National Health Information Database in Korea to identify patients who had diabetes and were diagnosed with colorectal cancer between 2002 and 2016. The total study population included 33,841 patients who were followed for an average of 4.7 years.

The researchers estimated patients’ medication adherence by using prescription data to calculate the proportion of days covered (PDC). Adherence to injectable medications, including insulin, was not measured. Patients with a PDC of at least 80% were considered to have high adherence, whereas patients below 80% were considered to have low medication adherence.

The investigators found that more than 80% of patients were taking more than 1 oral antidiabetic medication, but that less than 23% were in the high-adherence category. Compared with patients with high adherence levels, those with low adherence had a nearly 20% increase in their overall mortality risk.

Notably, the investigators did not have access to some clinical information, including cancer stage, which is an important factor to compare prognoses between different groups. Because of this, the investigators stratified the study population based on the type of cancer treatment they received.

Finally, the investigators noted that patients who received surgery, surgery plus radiotherapy, or surgery plus chemotherapy had a protective benefit if they had high adherence to their oral antidiabetic medications.

“Based on our data, less than 25% of patients were taking their diabetes medications as prescribed, suggesting that over 75% of diabetic patients with colorectal cancer could benefit by adhering to these prescriptions,” said senior author Aesun Shin, MD, PhD, in a statement.

Adherence to Oral Antidiabetic Medications May Improve Survival in Patients With Colorectal Cancer and Diabetes [news release]. American Association for Cancer Research; June 1, 2020. Accessed June 4, 2020.