Bristol-Myers Squibb Co. and AstraZeneca Plc’s new diabetes pill may cause breast and bladder cancer, according to U.S. regulators weighing whether to clear sales of the medicine.

While Food and Drug Administration staff said the drug is effective, they focused on safety concerns in a review of dapagliflozin released Friday ahead of a FDA advisory panel meeting Tuesday in Silver Spring, Md. New York-based Bristol-Myers and AstraZeneca of London have said they expect a final decision on approval by Oct. 28.

Dapagliflozin would be the first in a new class of treatments called SGLT2-inhibitors that work by letting patients excrete excess blood sugar in their urine. Indianapolis-based Eli Lilly and Co., Johnson & Johnson, Boehringer Ingelheim GmbH and Astellas Pharma Inc. are among the companies pursuing similar drugs.

Bristol-Myers Squibb and AstraZeneca said in June that more bladder and breast cancers were seen in patients taking the new medicine instead of a placebo in studies. Regulators have increased scrutiny of diabetes pills since GlaxoSmithKline Plc’s top-selling Avandia was tied to heart attacks in 2007 and was ultimately forced off the market in Europe and severely restricted in the United States.

“Several unexpected safety issues identified in this clinical development program were of sufficient concern to FDA to merit discussion of their impact on the overall benefit-risk consideration of dapagliflozin,” agency reviewers said in the report.

Nine cases of bladder cancer occurred in male patients who took dapagliflozin, compared with one case among people treated with a placebo. Breast cancer occurred in nine patients who took dapagliflozin, and one patient in the control group. FDA staff also said the drug was less effective in patients with impaired kidney function.

“We believe pretty strongly that this will be an uphill battle for the panel and that FDA will almost definitely seek more information before approving dapagliflozin,” Seamus Fernandez, an analyst at Leerink Swann in Boston, said in a report to clients.

An estimated 25.8 million people in the U.S. have diabetes, mostly the Type 2 form tied to being overweight and sedentary, according to the National Institutes of Health. The disease is caused by an inability to use insulin to break down blood sugar into energy and can increase the risk of heart disease, stroke and kidney damage. Medicines are used to lower blood sugar.