Does Lantus (insulin glargine) increase the risk of breast cancer?

We've seen some troubling information emerge in the world about diabetes. We now have controversy regarding the saftey of Lantus (insulin glargine). With the heading, "Lantus insulin: a possible link with cancer which requires further investigation," we see a press release from Diabetologia titled, "Possible link between insulin glargine and cancer prompts urgent call for more research." The next line says: "But experts stress patients should not stop using insulin and consult their doctor if concerned."

The press release starts with: "The European Association for the Study of Diabetes (EASD) today makes an urgent call for more research into a possible link between use of insulin glargine (an insulin analogue, brand name Lantus) and increased risk of cancer, following evidence from studies in Germany, Sweden and Scotland. However, until this further research becomes available, these experts are stressing that patients with diabetes taking Lantus should continue to do so, although some might wish to consider alternative types of insulin. The studies are reported in Diabetologia (the journal of EASD)."

What were the findings? "Professor Edwin Gale, Editor of Diabetologia, and Professor Ulf Smith, President of EASD, realised the significance of these findings but wanted them replicated in other studies from other European countries before announcing them formally. Studies were thus carried out using databases from Sweden, Scotland, and the UK.

• The Swedish study found that compared with patients on insulins other than Lantus insulin, patients on lantus insulin alone had double the risk of breast cancer.
  
• The Scottish study found a non-significant increased risk for breast cancer specifically.
  
• The UK study found no link between insulin glargine and cancer."

Yet these studies have some significant limitations:

• Although the data were adjusted for a number of variables, the characteristics of the groups of patients taking lantus insulin alone (generally older, higher blood pressure, more overweight) were different to those on other forms of insulin. Thus any difference in cancer risk could be attributed to the pre-treatment characteristics of the groups, rather than the treatment itself.
• The numbers of cases of breast cancer in the Swedish and Scottish studies were very small, meaning the findings could have occurred due to chance.

So, how does that make you feel? Maybe if you're Swedish or Scottish, you may feel concerned. If you're British, you may feel relieved. Sounds silly, doesn't it? When we have conflicting data, the topic becomes a controversy. We have no causal data. We have no consensus statements. We have no definitive stances from major diabetes associations. What does the American Diabetes Association (ADA) have to say about this? We don't know yet. Hence, we now have a controversial topic on our hands. The investigators recognize that this is a controversy and they stress (once again) "that patients should not stop using insulin and consult their doctor if concerned."

The EASD released a statement, which reads: "These studies are described and commented on in greater detail in the webcast by Professor Ulf Smith (University of Göteborg, Sweden), and Professor Edwin Gale (University of Bristol, UK). EASD emphasises that the studies reported are far from conclusive, but they do indicate the need for further investigation of this issue..."

To read the full press release on Diabetologia, click here.