GENTOFTE, Denmark - Diabetics who take insulin have a higher risk of developing cancer, according to Danish researchers who said they can't explain the link.
Patients on insulin were 50 percent more likely than the general population to get cancer, researchers led by Bendix Carstensen from the Steno Diabetes Center in Gentofte, Denmark, wrote in an abstract of the study posted on the Web site of the European Association for the Study of Diabetes.
The findings are to be presented next month in Stockholm at the association's annual conference.
The researchers said people with diabetes already have a higher risk of cancer, and the tumor development observed in this study may not be caused by insulin itself, said Mr. Carstensen, senior statistician at the center.
It may be the result of contributing causes common to cancer, diabetes, and insulin use, such as obesity, he wrote in the abstract.
The study, conducted on the Danish population, is the largest of diabetes and cancer incidence so far, Mr. Carstensen said.
"People who are on insulin have a higher risk of developing cancer," Mr. Carstensen said yesterday. "But what the reason for that is, it's not clear from this study nor from any other study."
To follow diabetes patients and see how many developed cancer, researchers created links between the Danish National Diabetes Register and the Danish Cancer Register.
They compared their findings with data on tumor occurrence among people not suffering from diabetes, according to the abstract.
They observed a total of 30,000 cancer cases among diabetics, including tumors of the digestive tract, liver, and pancreas.
Diabetes causes blood-sugar levels to be higher than normal. Insulin, a hormone made in the pancreas, helps convert blood sugar into energy.
Diabetics either don't produce enough insulin naturally or their bodies have trouble using it properly.
Glucose-lowering therapies such as Sanofi-Aventis' Lantus, the first once-a-day form of insulin, have become standard care for people who can't control their blood sugar levels with diet or exercise.
The new study is not the first to try to shed light on the possible link between insulin use and higher cancer risk.
Last year, Ralph DeFronzo, a researcher at the University of Texas Health Science Center, said that studies would show Lantus was tied to cancer.
In Paris, shares in Sanofi slumped after that call.
The research, published in the journal Diabetologia, delivered mixed results, and the Food and Drug Administration said it didn't prove a link.
Another study, based on 1,500 patients and published in June in the journal Diabetes Care, also tied insulin glargine, the chemical name for Lantus, to a higher tumor risk.
Sanofi, France's biggest drug maker, remains confident of the safety of Lantus, Chief Medical Officer Jean-Pierre Lehner said. The study in Diabetes Care is unclear and "lacks precision," he said.
It can be "methodologically challenged," Sanofi said at the time.