Diabetologia, a journal of the European Association for the Study of Diabetes (EASD) published online, says that data from four clinical studies has revealed a possible link between a long-acting insulin analogue, insulin glargine (brand name Lantus from sanofi aventis) to cause cancer. This follows evidence from studies in Germany, Sweden, UK and Scotland covering 3,40,935 people with diabetes.

As a basis for such a possible link, an accompanying editorial explains that certain insulin analogues have a structure making them more likely to bind to the IGF-1 receptor which is known to be involved in promoting tumour growth.

The disturbing result is that malignancies were found more frequently in patients treated with glargine than in those prescribed a comparable dose of human insulin. The research identified a statistically significant link between patients who had used Lantus insulin and those who had been diagnosed with cancer. Compared with people using similar doses of human insulin, out of every 100 people who used Lantus insulin over an average of about one-and-a-half years, one additional person was diagnosed with cancer.

Of particular interest in this study was the finding that the increased risk of cancer with Lantus was dose-dependent. Thus for patients who took a dose of 10 U, Lantus insulin alone increased the risk of cancer by 9 per cent compared with human insulin. But for a dose of 50U, the increased risk was 31 per cent.

According to Institute for Quality and Efficiency in Health Care (IQWiG), which in collaboration with 'Wissenschaftliches Institut der AOK' (WIdO), the research institute of the German Local Health Care Fund, analysed the data of almost 130,000 patients with diabetes in Germany, the overall indications of a risk from glargine have now intensified to such an extent that the burden of proof has been reversed for precautionary reasons. As long as reliable studies do not prove the safety of glargine compared to human insulin, the drug should only be used if there are particularly important reasons for doing so. The Swedish study that was done after the German study, found that patients on Lantus alone had twice the risk of breast cancer than patients on insulins other than Lantus.

Concern over Lantus was stoked by Ralph DeFronzo, a diabetes researcher at the University of Texas Health Science Center, who predicted an 'earthquake' event that might prompt doctors to not 'feel so comfortable with glargine' insulin, according to a transcript of the call.

The seriousness with which the market has taken this news can be judged by the fact that Sanofi shares slumped 12 per cent over the past two days, knocking 7.7 billion euros ($10.8 billion) off its market value.

"The finding linking cancer to glargine is specific to glargine as is clear from the studies published in Diabetologia, by EASD. In view of patient safety, clinicians should evaluate safer options based on available evidence like genotoxicity and mitogenic data."