Small study results released at yesterday’s Genitourinary Cancers Symposium in San Francisco showed that 15% patients taking Pfizer’s Sutent suffered heart failure, a rate higher than in clinical trials of the drug.

Seven of 48 patients receiving Sutent experienced heart failure, according to the study lead by researcher Dr. Melinda Telli of the Stanford University School of Medicine.

The small 48-patient study, which tracked patients from 2004 to 2007, was not a clinical trial.

Telli said that although the study was limited by the numbers it is possible that the true incidence of heart failure could be even higher. She advised that doctors should conduct routine monitoring of Sutent patients to detect problems with heart function.

Barbara Ryan, analyst for Deutsche Bank North America, said in a published report that results of the study “probably warrant further investigation,” but it’s difficult to draw any conclusions, “given the small size of the study.”

Sutent is approved by the FDA in treatment of cancer of the kidney and digestive system. Sales of the drug for 2007 were $581 million, up 166% from $219 million the previous year.

A Pfizer spokeswoman told website CNNMoney.com that the company has not had an opportunity to review the data and stressed that cardiovascular events are acknowledged on Sutent safety labels, along with recommendations for monitoring patients with cardiac risk factors.