Two popular diabetes drugs are being scrutinized after some researchers warned that their prolonged use may make diabetics more susceptible to multiple cancers.

The potential dangers of Byetta, manufactured by Amylin Pharmaceuticals and Eli Lilly & Co., as well as Novo Nordisk's Victoza, will be the highlight of the European Association for the Study of Diabetes conference in Lisbon, Portugal this week, Bloomberg reports.

Although the manufacturers claim the drugs, both of which belong to the category of GLP-1 therapies, are safe and have not been proven to increase patients' cancer risk, a review of database of side effects by researchers at the University of California at Los Angeles reportedly showed that patients who take Byetta and a similar medication made by Merk and Co. were six times as likely to develop pancreatitis, which raises the risk for tumors.

However, sales of GLP-1 drugs are rising as more doctors seek alternatives to older diabetes medications. GLP-1 drugs are made to mimic a hormone called GLP-1 in order to stimulate natural insulin production in diabetics.

While manufacturers insist their diabetes medications are safe, Peter Butler, a researcher at UCLA, told Bloomberg there are now several studies that imply the opposite.

There are now several animal studies as well as clinical reports from humans that taken together raise concern that there may well be serious unexpected side effects of the GLP-1 class of drugs on the pancreas, Butler said.

The drugs, according to Butler, may promote the unnecessary production of pancreatic duct cells that may then partially block the passage of digestive enzymes, which may cause local pancreatic inflammation - a risk factor for pancreatic cancer.

The GLP-1 drugs aren't the first diabetes medications to face major safety concerns. GlaxoSmithKline's Avandia, which was once the bestselling treatment for the ailment in the word, was banned in Europe and limited in the U.S. after it was found to bolster the risk for heart attacks.

Furthermore, Actos, made by Takeda Pharmaceuticals, was pulled from France in June after a study showed it could increase the risk of bladder cancer. In June, the Food and Drug Administration also concluded that using Actos for more than a year may be associated with a higher risk for bladder cancer, but the medication is still legal in the U.S.

About 346 million people across the globe have diabetes, according to the World Health Organization, which reports 3.4 million people died from the ailment in 2004. The agency expects diabetes deaths will double by 2030.

The Centers for Disease Control and Prevention reports diabetes affects 25.8 million people in the U.S., translating to 8.3 percent of the population. It is the seventh leading cause of death in the nation.