Glucophage (metformin), an oral diabetes medicine that helps control blood sugar levels, does not improve survival among patients with type 2 diabetes and malignant pleural mesothelioma, contrary to what has been described in diabetic patients with other types of cancers.

The results come from a retrospective study published in Lung Cancer, titled “Metformin and survival of people with type 2 diabetes and pleural mesothelioma: A population-based retrospective cohort study.”

A number of studies have shown strong association between diabetes and cancer incidence and mortality, with 8 to 18 percent of cancer patients having diabetes. In addition, pre-existing diabetes has been shown to increase cancer mortality by as much as 41 percent.

Metformin, which is also marketed as Glumetza, Fortamet, and Riomet, is widely prescribed as a first-line therapy for type 2 diabetes, and is believed to have anti-cancer effects, leading to improved survival in diabetes patients with several types of cancer. Studies have demonstrated this in non-small cell lung cancer, where Glucophage inhibited tumor cell growth and enhanced the effects of radiotherapy and chemotherapy.

Given the lack of studies addressing whether Glucophage increases survival in patients with diabetes and malignant pleural mesothelioma, which is associated with very poor outcomes, the researchers conducted a retrospective cohort study in type 2 diabetes patients diagnosed with pleural or unspecified mesothelioma included in Scottish population-based diabetes and cancer data sets.

The researchers hypothesized that, similar to what was found in lung cancer, Glucophage would also improve the survival of these patients. But their results proved otherwise.

Among the 300 patients with type 2 diabetes and mesothelioma, 148 had used Glucophage, and 290 died during a median follow-up of 7.5 months. Although the researchers found that users survived for a median of 8.8 months and non-users for a median of 6.5 months, the results were not statistically significant.

This lack of association between Glucophage administration and improved survival was still observed, even after the researchers adjusted their data for age, sex, diabetes duration, socio-economic status, and other anti-diabetic medications. In addition, non-statistically significant associations were also identified even when patients took Glucophage in the year before mesothelioma diagnosis, or used Glucophage for more than a year.

The researchers note that the small sample size and the absence of data regarding mesothelioma stage or sub-type are limitations of their study, possibly accounting for imprecise estimates.

“Other limitations include the lack of information on comorbidities, glucose control, and mesothelioma treatments in the dataset. As a result the possibility of confounding by these factors remains,” Hongjiang Wu, from the University of Edinburgh, and colleagues wrote.

Nevertheless, the researchers believe that so far there is no evidence to support trials of Glucophage in patients with mesothelioma.

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