Debate rages over whether Lilly’s Byetta lifts cancer risk

Amylin Pharmaceuticals Inc. and Eli Lilly and Co.’s Byetta and Novo Nordisk A/S’s Victoza, two insulin-raising drugs, don’t appear to carry an increased risk of cancer, according to a German researcher.

“The bulk of findings tends to speak against such an association,” Michael Nauck, head of the Diabeteszentrum Bad Lauterberg in Harz, Germany, said in an interview. “There is no general agreement.”

Nauck debated Peter Butler of the University of California at Los Angeles at the European Association for the Study of Diabetes meeting Friday on whether so-called GLP-1 therapies increase cancer risk.

Sales of the drugs may be hurt should Butler’s view prevail that there are signs of increased cancer from the drugs. He and other UCLA researchers said in a study this year that a review of a database of side effects showed patients taking Byetta and a Merck & Co. drug had a higher chance of developing pancreatic or thyroid tumors.

The treatments are safe and there’s no evidence of a higher cancer risk, according to the manufacturers of the drugs. Doctors are increasingly turning to GLP-1 medicines to fight diabetes, which affects 366 million people worldwide, killing one every seven seconds, according to an estimate by the International Diabetes Federation. The treatments mimic a hormone called GLP-1 to stimulate natural insulin production in diabetics.

Sales of the daily shot Victoza more than quadrupled in the second quarter to $230 million. Byetta, a twice-daily injection, had worldwide sales of $710.2 million last year.

In a study published in the journal Gastroenterology in July, Butler and the other researchers said the GLP-1 drug class “could have serious unintended and unpredicted side effects.”

Their analysis of the U.S. Food and Drug Administration’s database of reported adverse events from 2004 to 2009 found that patients taking Byetta and Januvia, a Merck drug belonging to a separate new class of diabetes drugs, had a six-fold increased chance of pancreatitis.

The researchers also found a 2.9-fold greater rate of pancreatic cancer and an increased risk of thyroid cancer for diabetics using exenatide, the chemical name for Byetta, according to a UCLA statement handed out to reporters yesterday. Sitagliptin, as Januvia is also known, was associated with a 2.7-fold higher rate of pancreatic cancer, compared with other therapies. The study didn’t look specifically at Novo’s Victoza.

“The data we have so far makes the question sufficiently robust that it has to be answered,” Butler said in an interview in Lisbon. “Hopefully this debate will raise the awareness of the scientific community, so that people will be motivated to join in the research.”

Several researchers and drugmakers including Novo Nordisk criticized Butler’s analysis, saying the FDA’s voluntary reporting system can’t be used to calculate the incidence of side effects.

Butler’s study is an “erroneous analysis” and its results “are really not reliable at all,” Matteo Monami, a physician at the University of Florence and Carreggi Teaching Hospital in Italy, said in an interview.

Monami on Thursday presented a study showing no increase in cancer or pancreatitis for so-called dipeptidyl peptidase-4 inhibitors such as Januvia. Another study to be discussed today will show this drug class potentially has a protective cardiovascular effect, he said.

While the FDA database has limitations, it also offers advantages such as a large sample size, the fact that it is accessible to everyone and that it’s independent from companies that market the drugs, Butler said at Thursday’s press conference.

Diabetes is caused by a lack of insulin needed to convert blood sugar into energy. Regulators already have taken note of possible links between the new classes of diabetes drugs and pancreatitis and thyroid tumors. Pancreatitis is a risk factor for pancreatic cancer.

For Nauck, the data examined not only fails to establish a link between GLP-1 therapies and thyroid and pancreatic cancer. It also may show the drugs may protect against certain other forms of cancer, such as prostate tumors, he said.

“Looking at the same database and using very, very similar methods, I find evidence that some forms of cancer are reduced,” Nauck said during the interview.

Signals that GLP-1 drugs may potentially reduce prostate cancer in diabetics are “subject to the same sort of bias” as the signals found by Butler and colleagues, he said. “You can either believe both those findings or none of them,” Nauck added.

Some doctors say they’re limiting their use of the new drugs.

“There must be some restraint with new compounds such as GLP-1s and DPP-4 inhibitors,” Gerard Guillain, an endocrinologist in Nice, France, said. “I am not sure we are totally aware what happens with these drugs. I only prescribe them when it’s absolutely necessary. Otherwise I avoid them.”

Carl Johan Oestgren, a professor at the Department of Medical and Health Sciences at Linkoeping University in Linkoeping, Sweden, uses GLP-1 analogues “only for a few patients.”

“I don’t think there is evidence at all that GLP-1 analogues may induce cancer at this stage,” he said. Still, “when new drugs come to the market, it’s very important to be careful at the beginning.”

Lilly, Amylin, Novo Nordisk and Merck say their products haven’t been shown to cause cancer.

“To date the available data do not demonstrate that exenatide increases the overall risk of cancer in humans,” Indianapolis-based Lilly and San Diego-based Amylin said in e-mailed statements last week.

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