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February 25, 2015
Does Less Adherence to Diabetes Therapy Increase
Cancer Mortality?

Eindhoven, The Netherlands—Diabetes patients become less adherent to their glucose-lowering medications when they are diagnosed with cancer, according to a new study which also raised an important question: Does failure to follow their drug regimen help explain why diabetics have significant higher overall mortality risk than cancer patients without diabetes?

Most research on diabetes and cancer has focused on the influence of diabetes and glucose-lowering drugs (GLDs) on outcomes after cancer diagnosis, not on how cancer could affect outcomes associated with diabetes, including adherence to prescribed GLDs, according to the study published recently in the journal Diabetologia. The study was led by researchers from the Netherlands Comprehensive Cancer Organization in Eindhoven.

Authors note that one previous study found that breast cancer patients were less likely to take their diabetes drugs as directed after being diagnosed with cancer, but that study lacked a control group without cancer. In this study, the authors focused on changes in adherence to GLDs following a cancer diagnosis compared with similar diabetic patients without cancer.

To that end, researchers selected all new 52,228 users of GLDs from 1998 to 2011 from the Eindhoven Cancer Registry-PHARMO Database Network, which includes out-patient pharmacy data. Out of that, 3,281 cases with cancer and 12,891 controls without cancer during follow-up were included in the study; each group had a mean age of 68.

The Medication Possession Ratio (MPR) was used as an indicator for medication adherence. The data showed that, before cancer diagnosis, the MPR increased by 0.10% per month. Yet, in addition to a significant drop in MPR at the time of cancer diagnosis of –6.3%, MPR showed an ongoing, yet lower, monthly decline of –0.20% afterward.

The largest declines in MPR at the time of cancer diagnosis, in the range of 11% to 15%, were seen among patients with stage IV cancer disease and gastrointestinal or pulmonary cancers.

Medication adherence differed by cancer type, according to the study. No significant decline in MPR was noted at the time of diagnosis for prostate (+2.1%) and breast cancer (–0.5%), but large drops were seen among patients with esophageal, stomach, pancreatic, or liver cancer (–12.5%;), as well as pulmonary cancers (–15.2%).

Among those patients with large adherence drops, the MPR after cancer diagnosis decreased approximately 0.5% monthly, indicating ongoing declining medication adherence for esophageal, stomach, pancreatic, liver, and or pulmonary cancers.

The greatest declines in MPR at the time of cancer diagnosis were seen for liver and esophageal cancer, –35% and –19% respectively, while the largest ongoing decline in MPR of almost 1% each month was seen among patients with pancreatic cancer.

The higher the stage of cancer at diagnosis, the authors point out, the greater the decline in medication adherence. For example, for patients with stage IV cancer, the drop in MPR was –10.7%, while each extra month after cancer diagnosis the MPR declined an additional –0.64%.

“Users of GLDs with more lethal cancers might prioritize the fight against cancer over the effort required to have a good metabolic control for their diabetes,” the authors write. “The MPR might be a good indicator for medication adherence, although the physician could have advised the patient to stop the treatment with GLDs, which could not be investigated within the study. Reasons for stopping their treatment for diabetes are unknown—is it because of frequent hypoglycemic events due to cancer or intolerable oral intake of drugs, for example among esophageal or stomach cancer patients?”

The researchers suggest, however, that the lack of medication adherence—whatever the cause—could be a contributor to higher mortality rates in patients with both diabetes and cancer.

“The decline in adherence seen among users of GLDs with cancer might negatively impact survival and (partly) explain the established association between diabetes, cancer and mortality,” they note. “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?”

 


U.S. Pharmacist Social Connect