Sanofi’s Lantus, the world’s top-selling insulin with $4.7 billion in annual revenue, more than doubled the risk of developing cancer among people with diabetes, researchers said.
Diabetics who used Lantus had a 2.9-fold greater chance of cancer, while those who took the generic drug metformin had an 8 percent lower risk, according to the study presented yesterday at the San Antonio Breast Cancer Symposium. Researchers examined medical records of 23,266 patients in southern Sweden.
The researchers were unable to identify which types of cancer were most common among Lantus users, said Hakan Olsson, lead researcher and professor of oncology at Lund University. They plan to follow the patients, and investigate different forms of diabetes treatment including Novo Nordisk A/S’s long-acting insulin Levemir, to find any differences, he said.
“Women should be aware that diabetes and breast cancer may be related,” Olsson said in a telephone interview. “The diabetes itself could play a role in the development of cancer and now data is emerging that drug therapy may also be important in relation to cancer.”
It’s not the first time Lantus has been linked to cancer. The once-a-day injected insulin was found to raise tumor risk in two database reviews published in June 2009, while two others showed no ties.
In January, an investigation by U.S. regulators found there was no conclusive danger, and three trials are under way to resolve the issue. In the new Swedish study, a diagnosis of diabetes, regardless of treatment, raised women’s risk of developing breast cancer for four years.
The Swedish study released yesterday was too small and had flaws that make it impossible to definitively address any potential risk from Lantus, said Riccardo Perfetti, vice president for medical affairs at Sanofi Diabetes in Paris. The company is researching the question, with more robust results expected by the end of the year, he said.
“I find it surprising that today after so many scientific reports on this topic, we’re still discussing these very small studies,” he said. “Patients using insulin may be compared to patients not using insulin, which might be a gigantic methodological mistake. People using insulin are usually much older and have been diabetic for many years.”
A Sanofi study from Sweden, Norway, Finland, Denmark and Scotland is complete and will be submitted to health authorities this month, Perfetti said. A U.S. study will be finished in early 2012, while a final report from Europe will come later, he said. Those studies, involving more than 1 million patients, will help resolve any questions of risk, he said.
The company’s records, involving the equivalent of more than 38 million patients taking the drug for at least a year, show no danger, he said in a telephone interview.
A comprehensive review of studies released today at the World Diabetes Congress in Dubai showed there is no increased danger of breast cancer or any other tumor type among patients taking Lantus, Sanofi said in an e-mailed statement today.
Sanofi shares rose 2 percent to 52.84 euros in Paris trading. The stock has gained 10 percent this year.
The Swedish study is based on “uncontrolled retrospective analyses” and therefore is “very unreliable,” Mark Clark, an analyst at Deutsche Bank AG in London, wrote in a note to clients today. He has a “buy” recommendation on Sanofi shares.
Concern about a potential cancer link hasn’t slowed Lantus’s sales, which rose 12 percent to 3.51 billion euros ($4.7 billion) in 2010. It is Paris-based Sanofi’s best-selling medication and generates more than twice the revenue of Levemir from Bagsvaerd, Denmark-based Novo Nordisk. Pierre Chancel, head of the company’s diabetes division, said in September he expects Lantus to reach sales of almost 4 billion euros this year.
Doctors and patients should be aware that there may be a cancer risk from Lantus, Olsson said.
“We need more data to make definitive recommendations to patients,” Olsson said. “If I was a patient and I had a choice, I would already choose the one where don’t yet see any cancer risk,” he said.
The goal of the study was to determine how other health conditions influence cancer development. The researchers turned up some surprises, including an inverse relationship between cholesterol and cancer. High levels of the lipids known to raise heart risk seemingly protected against breast tumors, Olsson said. The researchers still have to determine if the women were taking drugs to lower their cholesterol levels.
Weight also provided an unexpected result. There was an inverse relationship between obesity and breast tumors at an early age, with overweight young women having a lower risk of cancer, the study found. After menopause, overweight women had a higher risk, Olsson said.