The Food and Drug Administration said Tuesday it saw a low cardiovascular event rate in clinical studies of liraglutide, a proposed diabetes drug being developed by Novo Nordisk Inc. (NVO), but raised concerns about a small number of patients who developed a type of thyroid cancer during clinical studies.

Liraglutide, a drug being developed to treat type-2 diabetes, faces a review by an outside panel of medical experts Thursday. The panel will be asked to vote on questions about safety and the outcome of those votes will amount to a recommendation about whether it thinks the agency should approve the product. The FDA usually follows its panels' advice but is not required to.

The FDA has been concerned about cardiovascular side effects of diabetes drugs since a research paper was published in 2007 linking GlaxoSmithKline PLC's (GSK) widely-used Avandia to increased risk of heart attack. The agency issued new guidance in December requiring drug makers to conduct more-stringent clinical trials for type-2 diabetes drugs to better assess heart-attack and stroke risks. The application for liraglutide was submitted last May before the guidelines were issued.

In documents prepared for the panel meeting that were released Tuesday, the FDAsaid while it saw a low cardiovascular event rate in clinical studies of liraglutide, it will ask the panel for advice on whether it "permits a reliable assessment of clinical safety."

The agency is also asking the panel about the development of certain thyroid tumors that were seen in rodent studies and whether they are relevant to humans.

The agency said in clinical studies there were five patients who developed papillary thyroid carcinoma among patients taking liraglutide and one case among a patient not receiving the drug.

The FDA said most of the reported thyroid cancers were "very small." The agency also said small thyroid tumors are commonly found in the general population.

Novo Nordisk, in a briefing document released by the FDA, said the thyroid findings may be "ascertainment bias." In at least one clinical study all patients underwent thyroid ultrasounds.

The company has proposed conducting a large post-marketing trial that would study cardiovascular outcomes as well as other potential side effects.

Novo Nordisk said liraglutide was effective at lowering blood-glucose levels compared to other diabetes drugs looked at in clinical studies. The company also said the drug helped some patients lose weight and lowered blood pressure.

Type 2 diabetes, which affects 23 million Americans, is characterized by high blood-glucose levels that result from the body's inability to use insulin.

Liraglutide is a long-acting form of a hormone known as GLP-1 that triggers the release of insulin in the body, which is needed to properly digest and use sugar from food. The drug is designed to be injected once daily. It falls into a class of drugs known as incretin mimetics and is similar to Byetta, by Amylin Pharmaceuticals Inc. (AMLN) and Eli Lilly & Co. (LLY), which is injected twice daily.

Amylin, Lilly and Alkermes Inc. (ALKS) are working on a form of Byetta that would be injected only once weekly, and the companies are expected to file a new drug application with the FDA by the end of June.

-By Jennifer Corbett Dooren, Dow Jones Newswires; 202-862-9294; jennifer.corbett@dowjones.com