UPDATE 1-Pfizer cancer drug Sutent linked with heart risks

(Adds Pfizer comment in paragraphs 18-19)

By Julie Steenhuysen

CHICAGO, Dec 13 (Reuters) - Pfizer Inc's (PFE.N) cancer drug Sutent may have toxic effects on the heart, U.S. researchers said on Thursday.

Nearly half of 75 patients with rare gastrointestinal tumors who took the drug in a clinical trial developed high blood pressure, 8 percent developed heart failure and two patients had heart attacks, according to a new analysis of clinical trial data.

The analysis, conducted by researchers at Children's Hospital Boston, the Dana-Farber Cancer Institute in Boston and Thomas Jefferson University in Philadelphia, suggests patients taking the drug -- and especially those with heart risks -- should be closely monitored.

"If a patient develops shortness of breath, fatigue and swelling of the feet and hands, they should seek medical attention," said Dr. Ming Hui Chen, a cardiologist at Children's, whose study was published in the Lancet medical journal.

Most of the patients in the study responded to medications to control their symptoms, she said.

The finding follows the discovery last year that the Novartis AG (NOVN.VX) drug Gleevec, a pill that transformed treatment for leukemia patients, caused heart failure in 10 patients.

Both drugs are tyrosine kinase inhibitors and the findings raise concerns that so-called smart drugs, which target specific signaling molecules inside cancer cells, may be interfering with signaling systems needed for the survival of normal cells, including heart cells.

"They may be inhibited by these smart drugs," Chen said in a telephone interview.

She and colleagues reviewed all heart events in 75 adults with gastrointestinal stromal tumors that had spread. They had been enrolled in a clinical trial in 2002-2004 looking at the safety of Sutent, known generically as sunitinib.

All patients in the study had developed resistance to Gleevec, or imatinib. All had normal heart pumping function before the study and none had a history of heart failure.

As the study progressed, six of the 75 patients developed heart failure and two had heart attacks. Nearly half of the patients who received what is now the U.S. Food and Drug Administration approved dose of the drug developed significant decreases in the heart's ability to pump blood.

And 35 out of 75 patients developed high blood pressure. Chen said that while hypertension is a common side effect of cancer drugs, the degree of hypertension was significant.

"I think because the magnitude is large it is really important that we identify it early and we treat it aggressively," she said.