Results of a retrospective cohort study of patients with diabetes mellitus and newly diagnosed colorectal cancer (CRC) suggested that good adherence to oral antidiabetic medications was associated with a reduced risk of death. These findings were published in Cancer Epidemiology, Biomarkers & Prevention.

Limited evidence suggests that modifiable lifestyle factors, such as maintenance of a healthy diet and a normal body mass index (BMI), as well as regular exercise, can improve the prognosis of patients diagnosed with CRC. The aim of this study was to determine whether the level of adherence to oral antidiabetic medications was associated with improved survival in patients with newly diagnosed CRC and a preexisting diagnosis of diabetes.

Data for patients with newly diagnosed CRC and preexisting diabetes with a record of 2 or more prescriptions for an oral antidiabetic medication prior to diagnosis of CRC were abstracted from the South Korean Health Information Database for the period covered by 2002 to 2016. Cancer stage was deduced based on type of treatment received, with patients receiving surgery only classified as having early-stage disease, and those treated with palliative chemotherapy or radiotherapy without surgery considered to have the most advanced disease.

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The level of adherence to oral antidiabetic medication was estimated using the proportion of days covered (PDC), defined as “the number of day with drug on hand divided by the number of days in the specified time period.” A PDC of less than 80% or 80% or higher was associated with poor and good adherence, respectively. 

Of the 33,841 patients included in the study, 7615 and 26,226 were classified as having good and poor adherence to oral antidiabetic medication, respectively. A comparison of the baseline characteristics of these 2 groups showed that those in the former group had a higher age at CRC diagnosis (68.7 vs 66.8 years; P <.0001), a higher likelihood of receiving surgical treatment only (61.5% vs 58.3%; P <.0001), and a lower likelihood of ever having received insulin (12.8% vs 14.2%; P =.002) or being a current smoker (7.9% vs 11.5%; P <.0001).

At an median follow-up of 4.7 years, multivariate analysis of medication adherence and risk of death among the overall group of patients with CRC with diabetes mellitus showed risk of death was reduced by 18% (hazard ratio [HR], 0.82; 95% CI, 0.78–0.86) for those patients classified as adherent to oral antidiabetic medications when patients with poor adherence to these medications were used as the reference group.

Additional multivariate analyses stratified by cancer site, sex, and metformin and insulin use showed similar findings irrespective of cancer site, and for both men and women, and metformin users and insulin users/nonusers. However, no significant association between adherence to oral antidiabetic medication and improved survival was observed for the subgroup of metformin nonusers.

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In addition, when patients were grouped according to type of treatment received, the reduction in risk of death with a higher level of adherence to oral antidiabetic medication was observed only for those patient subgroups receiving surgery with or without chemotherapy or radiotherapy.

In commenting on the results of this study, the study authors posited that “one possible explanation is that because these medications are mainly focused on improving hyperglycemia or hyperinsulinemia, which are the acknowledged mechanisms by which diabetes mellitus contributes to cancer progression, the better the adherence, the stronger the effect of improving the survival of patients with cancer.” They further added that these findings may relate to potential anticancer effects of metformin.


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;29:1120-1127.