Patients with diabetes were less likely to adhere to glucose-lowering drug treatment regimens after receiving a diagnosis of cancer, researchers of a study published in Diabetologia found.
“Although the impact of cancer was more pronounced among cancers with a worse prognosis and among those with more advanced [tumor, node, metastasis] stages, the difference in prognosis associated with these cancers seemed to only partly explain the impact of cancer on medication adherence,” the researchers wrote.
The study included all new users of glucose-lowering drugs from 1998 to 2011 from the Eindhoven Cancer Registry-PHARMO Database Network catchment area. During follow-up, patients with a primary cancer diagnosis were matched with eligible controls without cancer.
Researchers used medication possession ratio (MPR) to indicate medication adherence and segmented linear auto-regression analysis with interrupted time series to determine changes in MPR for cases vs. controls.
The final analysis included 3,281 patients with cancer and 12,891 controls without cancer from the 52,228 glucose-lowering drug users selected.
According to the results, MPR increased by 0.1% (95% CI, 0.1-0.1) per month before cancer diagnosis. At the time of cancer diagnosis, there was a significant decrease in MPR (–6.3%; 95% CI, –6.5 to –6.0), with the largest decreases observed in patients with stage IV disease and gastrointestinal or pulmonary cancers, which ranged from 11% to 15%.
“The MPR drop of 6% at the time of any cancer diagnosis translates to a difference of 2 days in a month that is not covered by the use of [glucose-lowering drugs] due to the diagnosis of any cancer,” the researchers wrote.
There was also a smaller, but ongoing, monthly decline in MPR after diagnosis (–0.2%; 95% CI, –0.21 to –0.20).
The researchers added that an MPR drop of 20% would be considered the cutoff for an adherent vs. non-adherent glucose-lowering drug user.
“Based on these values, it may be that the overall decline of 6% we observed may not be considered clinically important,” they wrote. “On the other hand, the decline in MPR observed in patients with more severe or advanced cancers may be considered clinically important.”
The researchers noted that the decline in adherence observed in glucose-lowering drug users with cancer might negatively affect survival and partially explain the established association between diabetes, cancer and survival.
“In future studies, the reason for the decline in MPR needs to be further elucidated among the different cancer types — is it the patient who prioritizes the fight against cancer or the advice of the physician to stop the treatment?” they wrote.