They found that patients taking TZD (thiazolidinedione) drugs - including pioglitazone (Actos) and rosiglitazone (Avandia) for more than 5 years had 2 to 3 times the rate of bladder cancer as patients taking sulfonylurea drugs.
Type 2 diabetics already face a slightly higher chance of blader cancer. The research team estimates that over that 5-year period taking the TZD drugs, there would be about 170 patients per 100,000 developing cancer, compared to 60 among those taking the sulfonyurea drugs.
TZD drugs such as Avandia and Actos account for about 20 per cent of the drugs prescribed to diabetics in the United States.
Prescriptions for Avandia have dropped sharply since it was linked to severe cardiovascular problems, however, Actos is still widely used. It is the 9th most prescribed drug in the country, with 15 million prescriptions each year. Doctors often prescribe it when a patient's diabetes won't respond to the drug Metformin.
The Penn study was funded by the National Institutes of Health and published online in the Journal of the National Cancer Institute.