The first study to suggest a link was a German study of 127,031 insulin-treated patients who used the treatment.
The researchers found that out of every 100 people who used insulin glargine over an average of about one and a half years, one additional patient was diagnosed with cancer.
The study also showed that the risk of cancer appeared to be dose-dependent. Patients given a 50U dose of insulin glargine were 31% more likely to develop cancer, but those taking a lower 10U dose had a 9% raised risk.
The findings of this study were followed up in studies carried out in Sweden and Scotland. The Swedish study found an increased risk of breast cancer among patients on insulin glargine, but the Scottish study found only a non-significant increased risk for breast cancer.
Additionally, a UK study failed to find any link between insulin glargine and cancer.
The European Association for the Study of Diabetes (EASD) concluded that patients should not stop taking insulin glargine on the basis of the findings of the studies.
Professor of diabetes at Bristol University Edwin Gale led the UK study, and edits Diabetologia, the journal that published all four studies. He said: ‘Our studies establish that there is a clear case for urgent investigation of a possible link between glargine and cancer.
‘We think this can be done in a short time frame with access to larger registries and meta-analysis of the data.'
The formal advice, therefore, to patients on glargine is to keep going for the time being until these issues are put to rest, said Professor Gale.
Jean-Pierre Lehner, chief medical officer for sanofi-aventis, which markets Lantus, said: 'We consider that the results of these patient registries are not conclusive.'
- Read this week's issue of GP dated 10 July for the full version of this story.
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